Wednesday, November 29, 2023

Geology in Pop Culture - The Rescuers Down Under

 Geology in Pop Culture

Released in 1990, The Rescuers Down Under continues the escapades started in 1977's The Rescuers. However, in this adventure our favorite mice, Bernard and Bianca, travel down to the Australian outback (not the steakhouse). Here, they find that the villain of the story, the poacher Percival C. McLeach has kidnapped a boy, Cody, while hiding out in some abandoned opal mines.

 

So what exactly is opal anyway?

Different types of Australian opal varieties. Image courtesy of BlackOpal Direct. 

Opal (SiO2.H2O) is a mineral that forms from the packed spheres of silica (SiO2), also known as the mineral quartz. Opal is a hydrated form of silica where water has been shown to include between 3 and 9% of the total mineral structure. Unlike many minerals, because of how it is formed, opal is amorphous, or without form. This means that there is no crystal structure or cleavage that is seen in most other minerals. Opal forms through the processes of solidification of gelatinous or liquid silica within cracks and voids of other rocks. 

Since the opals are created by spheres of silica and water, the size of the sphere's dictates the colors that are produced. These colors are refracted through the opal like a prism, with larger spheres yielding red or orange, and smaller ones radiating blue. However, this is only the case with precious opals, the more gem quality ones. Most opals, ~95%, are referred to as common opals. These are opals that do not have the "play-of-color" expected in opals as seen in the image above. Although still beautiful, they are harder to identify than the precious opals. 

Location of Australian Opal Mines. Image courtesy of Opals Down Under. 

Despite being found around the world, it turns out that ~95% of the world's supply of precious opals comes from Australia. The opals started to form during the Cretaceous period when there was a large inland sea across Australia. During this time silica rich sands were deposited along the shorelines, then 30 million years ago, during the Tertiary, deep weathering of these sediments within the Australian Artesian Basin released large amounts of soluble silica into the groundwater. This silica traveled into the cracks and fissures in the Cretaceous age rocks where it was stopped by an impermeable layer below. Staying in the cracks and fissures, the opal deposits formed veins, often trapping fossils that also happen to be in the sedimentary rocks such as leaves, dinosaurs, small mammals, and marine reptiles such as Eric the Pliosaur. 

Eric the opalized pliosaur. Image courtesy of Opal Auctions. 

Most of the opal mines in Australia are a type known as open-cut. This means that they basically dig down to the source of the deposit, in this case opal, and clear out anything above it, forming a quarry or pit. This limits the dangers of enclosed mine spaces, allows you to find smaller deposits easier, is much faster with heavy machinery, but is also much, MUCH, more damaging to the environment, destroying literally everything to get to the deposits. 

In The Rescuers Down Under though, they are clearly not in an open-cut mine, they are underground mines. There are some underground opal mines that are found within Australia. One of these locations is the town of Mintabie, found near the north-central portion of the South Australian state. And although they did use open-pit mining in Mintabie, they also had quite a number of underground mines as seen in the picture below.

Mintabie Opal Mines. Image courtesy of Opal Auctions. 

What makes Mintabie interesting is that the mining heyday here was in the 1980's. Even though opals had been know from here since the 1920's, production increased starting in 1976 with the addition of mining equipment able to break through the hard sandstone. During the 1980's, production here was the largest in all of Australia with a peak during 1988. However, after 1988, production quickly declined resulting in lots of abandoned opal mines. 

Warning sign in The Rescuers Down Under

This timing of the opal mines being abandoned during the late 1980's correlates strongly with The Rescuers Down Under, which would have been starting to be in production probably ~1988. Seeing these abandoned opal mines pop up all over the place would have been a good impetus to a setting for their movie. 
at No comments:
Labels: , ,

Monday, November 27, 2023

Geology of the National Parks in Pictures - New River Gorge National Park & Preserve

My next post about the Geology of the National Parks Through Pictures is from my undergraduate years when we traveled the national parks during spring break.  

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

-----------------------------------------------------------------------------

New River Gorge National Park & Preserve

Another park that is within the Appalachian Mountains, the New River Gorge has a similar geological history as other nearby parks like Shenandoah National Park to the east and the Great Smoky Mountains to the south. It also traverses some of the same rock types as the Gauley River National Recreation Area a short distance to the north, however since the New River Gorge is much larger and deeper than the Gauley River valley, the rocks exposed are slightly older (although they also overlap). 


The New River Gorge cuts through Carboniferous Age deposits from the Upper Mississippian age Bluefield Formation (~325 million years old) up through the Middle Pennsylvanian Allegheny Formation (~312 million years old). 

Geology of the New River Gorge National Park & Preserve. Map courtesy of the NPS. 

The different formations are groups of rocks made up of members that were deposited in similar environments. Although the water levels fluctuate up and down during this time interval, overall North America is moving towards Africa in this time period as the Iapetus Ocean was closing up towards the east. Eventually North America will meet up with Africa to form the supercontinent Pangea, but we haven't gotten there yet when these rocks were deposited.

Geological map units for the New River Gorge National Park & Preserve. Courtesy of the NPS. 

The rock units here, as well as at Gauley River NRA, dip towards northwest in a direction that essentially follows the course of the river. One of the oldest formations, the Hinton Formation, was deposited along the coast, with both marine and freshwater deposits represented. It is made up of shales and siltstones, with lesser amounts of sandstones and limestones. It gets up to 1,000 feet thick within the gorge. 


Geologic Profile of the New River Gorge. Image courtesy of WVGES. 


Above the Hinton Formation, the Bluestone Formation is what is known as a regressive sequence, where the sea level slowly went downwards until there is a paleosol (ancient soil) deposited before the Pocahontas Formation starts to be deposited. The paleosol represents an unconformity, which is a buried erosional surface, and signifies the transition from the Mississippian to the Pennsylvanian. Above the Pocahontas Formation is the New River Formation, which is partially seen at the Gauley River NRA. This again represents a coastal environment and the last coastal environment deposited within the region.


The New River itself is often designated the "second oldest river in the world," however this is difficult thing to actually determine. We know that the oldest rocks that the New River erodes through are ~310 million years old, so the river must be younger than that. 




It is also estimated that the river is at least 3 million years old based on glacial evidence that the New River follows the same course as the pre-glacial Teays River a river that used to flow towards the northwest and eventually was the ancestor to the lower reaches of the Illinois River. The Teays River, and eventually the New River, is the only river to cut across the Appalachian Mountains. This is because it predated the mountains and was able to cut down through them as they were lifted up, much like the Colorado River cutting out the Grand Canyon or the Black Canyon of the Gunnison. Estimates for the age of the New River therefore fluctuate between 3 and 310 million years, quite a variance.  


Along the New River Gorge, with the steep sided cliffs due to the abundance of sandstone deposits forming ledges, there are a number of picturesque waterfalls. I believe this is Cathedral Falls, which starts far above me in the picture, tumbling over the New River Formation's Upper Nuttall Sandstone. 

But while there are some of the largest waterfalls in West Virginia within the New River Gorge, there are also smaller waterfalls, that flow down many of the shale deposits along the gorge's depth. 


References
at No comments:
Labels: ,

Thursday, November 23, 2023

Geology of the National Parks in Pictures - Gauley River National Recreation Area

My next post about the Geology of the National Parks Through Pictures is from my undergraduate years when we traveled the national parks during spring break.  

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

-----------------------------------------------------------------------------


The first couple of national parks that my future wife and I visited were in West Virginia, hence the reason I don't have many geologically themed photographs. Gauley River National Recreation Area is located within the Appalachian Mountains, much like Shenandoah National Park to the east and the Great Smoky Mountains to the south, so the geological formation of the region would follow a similar path.

Looking downstream the Gauley River from the Summersville dam

The Gauley River flows from east to west across West Virginia until it eventually meets up with the New River. Within the Gauley River NRA, the river cuts through Lower Pennsylvanian (~320 million years old) New River Formation rocks, specifically the Upper Nuttall Sandstone and some undifferentiated deposits below the Upper Nuttall and above the Upper Raleigh Sandstone. 

Bedrock Geologic Map of the Gauley River NRA. Image courtesy of the NPS. 

The Upper Nuttall Sandstone, along with the rest of the New River Formation, was deposited along the western coastal edge of the Iapetus Ocean as Pangea was slowing being formed and North America and Africa were barreling towards each other. The sandstone deposits themselves represent the beach/barrier island complex of the region. The sandstone layers are mixed with shale layers that are intermingled with several coal seams. These coal seams represent areas where lagoons formed when the barrier islands were located further to the east, allowing abundant live to thrive in a swamp-like environment. The New River Formation is the final gasp of coastal deposits in the area as the ocean fully closed up shortly after this.   

Summersville Dam

The Summersville Dam, seen here, is actually located just upstream of the National Park boundary along the Gauley River, however because of that it has a tremendous impact on the water flow through the park. Dam's have historically not been the best for the environment, completely disrupting the traditional flow of water, sediment, and wildlife that thrives in such an environment. However the construction of such dams also provide a much needed service for the people that live in the region. The construction of the Summersville Dam helps control flooding that was destroying nearby communities as well as provide a renewable source of energy through their hydroelectric plant.  

Also, interesting item of note, dams are typically named after the nearest town, however the nearest town was called "Gad" and it was agreed upon that the second closest town's name would be used instead. 

References
at No comments:
Labels: ,

Monday, November 20, 2023

Geology of the National Parks in Pictures - Shenandoah National Park

My next post about the Geology of the National Parks Through Pictures is from my undergraduate years when we traveled the national parks during spring break.  

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

-----------------------------------------------------------------------------


Much like the Great Smoky Mountains to the south, Shenandoah is formed by a small part of the Appalachian Mountains. 


The Appalachian Mountains are an amazing mountain belt because you can easily see the geology any time you pull up an aerial image of the region (like in Google Earth).

Google Earth aerial imagery of the central eastern US

The flow of the mountains from central Pennsylvania through western Virginia (where Shenandoah is located) to eastern Tennessee and western North Carolina is a perfect visual for the impact that produced them when North America collided with Africa. However, there are some events that took place before the Appalachian Mountains were formed. 

Granodiorites of the Pedlar Formation at the Hazel Mountain Overlook

As was the case for the Great Smoky Mountains, the oldest rocks within Shenandoah National Park are about 1.1 billion years old. These rocks formed during what is known as the Grenville Event and are known in the park as the Old Rag Granite and a gneiss called the Pedlar Formation (pictured above), The Grenville Event was the mountain building event (orogeny) which occurred during the formation of the Rodinia Supercontinent.  

Geological map of Shenandoah National Park. Full size available on the USGS website.

The Pedlar Formation and the Old Rag Granite make up the majority of the outcrops through the central portion of the park.

Big Meadows

As Rodinia started to split apart, or rift, lava poured out, forming the Catoctin Formation which is made up primarily of a metamorphosed basalt known as greenstone. The rifting continued until there was an ocean separating North America from Africa, much like today. This ocean is known to geologists as the Iapetus Ocean. Because of the hardness of the Catoctin Formation and its location within the park, many of the waterfalls are formed flowing over this formation. Big Meadows, as seen in the picture above, is located right atop 1,800 feet thick deposits of the Catoctin Formation. Along the edge of Big Meadows is Dark Hollow Falls, which drains the meadows as it falls over the Catoctin Formation. 


Erosion of the Grenville Mountains produced sediments that were deposited within the Iapetus Ocean, forming the rocks that would later make up much of the Appalachian Mountains. These include Cambrian and Ordovician age limestones, sandstones, and mudstones. Then around 470 million years ago, during the Ordovician, the continents took an about face and started to head towards one another again. 

Geologic map of the eastern US. Image courtesy of geologictimepics.com.

This eventually ended when North America plowed into Africa creating Pangea, the next in the supercontinent line. This collision uplifted the Appalachian mountains and created the great mountain imagery as we can see in the aerial and geological map above. Around 200 million years ago, in the Jurassic, Pangea started to break apart, creating the Atlantic ocean as well as eventually putting the continents in the configuration as we know them today. During the breakup, several Jurassic age dikes, volcanic intrusions, were formed and can also be seen in various locations within the park. Over time the Appalachian Mountains had slowly eroded to shadows of their former glories but the former grandeur of of them can still be glimpsed in the aerial imagery.  

References
at No comments:
Labels: ,

Friday, November 17, 2023

Geology of the National Parks in Pictures - San Antonio Missions National Historical Park

My next post about the Geology of the National Parks Through Pictures is from when I lived in Texas and we drove around exploring the national parks of the state.  

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

-----------------------------------------------------------------------------


San Antonio Missions is comprised of four missions that stretch out to the south of San Antonio along the San Antonio River. Starting north to south the missions are Mission Concepción, Mission San José, Mission San Juan, and Mission Espada. A fifth mission in the area, Mission San Antonio de Valero, better known as the Alamo is not part of the park but likely has a similar building history.

Mission Concepción

Built in the late 1700's, all of the missions seemed to have been built from the same building stones that were all available within the region. It appears that there were three primary stones chosen in the construction. Near the Mission Concepción is a quarry that was used to obtain the walls for the missions. The stones found here are a calcareous sandy tuffaceous limestone.  

Mission Concepción

McDowell, 1997 recounts the historic observations of these building stones from Ferdinand Roemer when he traveled to the San José Mission in 1846. He stated that one of the stones is ...
"... a light, porous, tufaceous limestone or travertine, which is also found in many parts of Germany, ... where it is valued highly as a building material on account of its lightness. This stone formation finds its particular origin in the deposits of springs containing lime. The cupolas and arched ceiling of the churches in the Missions are built of this material."
Mission San José

The carved elements of the building however come from a limestone that is much softer and purer. Romer stated this about that stone:
"The other stone used is a greenish gray limestone, containing clay, which has the peculiar property of being almost soft enough to be cut with a knife when taken from the quarry, but later hardens when exposed to the air. This peculiar mineralogical product is mentioned in several writings as being found in the region of San Antonio. This limestone, whose geological age can be determined by the numerous fossils, - particularly species of the family Exogyra,-enclosed in it, belongs to the Cretaceous formation and is found in several places in the neighborhood of San Antonio."
Mission San José

Based on the inclusion of Exogyra (a Cretaceous age oyster) as well as other factors and fossils within the limestone, it can be assumed that this ornamental limestone was from the Austin Chalk Group, an Upper Cretaceous formation deposited between 89 and 84 million years ago. Formed in the shallow to deep marine deposits along the northern edges of the Gulf of Mexico, the Austin Chalk Group is a series of different formations of which the chalk itself is only part. In the chalk, the majority of the rock is almost solid fossils with Exogyra only being a small percentage. The majority of the fossils are those of coccoliths, which are the microscopic shells of organisms called coccolithophores.

Mission San Juan

The limestone that had been used for the majority of the building's construction was also used as a mortar to cement the building blocks together since when wetted, the limestone dust dried hard as concrete.

Mission San Juan

There is a possibility that other local stones were also used including the local Anacacho Limestone, Pecan Gap Chalk, and Edwards Limestone.

Mission Espada

The final distinct building stone is a red sandstone. Although I can't find a positive identification for the sandstone, the sandstone used in the building is strongly cross bedded and may perhaps be the local Escondido Sandstone or Indio formation.


Mission Espada

Regardless, there is a lot of geology embedded in this park.

References
at No comments:
Labels: ,

Wednesday, November 15, 2023

Geology of the National Parks in Pictures - Alibates Flint Quarries National Monument

My next post about the Geology of the National Parks Through Pictures is from my move back from Texas to live in Buffalo for a few years.  

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

-----------------------------------------------------------------------------


The Alibates Flint Quarries National Monument is nestled up right next to the Lake Meredith National Recreation Area, so it is an easy two for one National Park stop.  

Located in the panhandle section of Texas, this area is known for it's extensive plains and the hard caprock that covers most of the region. The Red Beds of the region were deposited during the Permian Period, approximately 260 million years ago. The rocks deposited in these two parks include sandstones, siltstones, and mudstones, as well as gypsum and dolomite deposits. The red beds are made up of the Whitehorse Sandstone, Cloud Chief Gypsum, and Quartermaster Formation. The red in these red beds are produced by small amounts of iron oxide, AKA rust, mixed into the rock units.  

Upper geology layers found at Alibates Flint Quarries. Image courtesy of Quigg et al., 2011.

The red beds, ending with the Whitehorse Sandstone on the top, are all very soft deposits where any significant amount of rain can easily erode away the rocks. However the arid environment of the region helps preserve these softer beds, as well as the harder, more erosion resistant "caprock" that was deposited on top of the red beds. 


Over time the sea level slowly rose, eventually inundating this region under a shallow sea. Once the sea transgressed into the region, deposition of the Alibates Dolomite started and was produced from the plant and animal life living in the water (plankton, shelled animals, algae, corals). Dolomite is a variety of limestone where the primary mineral is dolomite (CaMg(CO3)2) instead of calcite (CaCO3). While calcite and dolomite for the most part are nearly indistinguishable to the naked eye, dolomite is generally less dissolvable than calcite, has a slightly higher hardness, and the crystals of dolomite typically have a slight curve to them while calcite surfaces as generally flat. The deposition of the dolomite layer created a "caprock" to the softer red beds below and can be seen in the photo above towards the top of the red slope surface. 

The Alibates Dolomite caprock creates flat areas known as mesas (Spanish for table), which are periodically broken up by cracks in the dolomite and stream erosion. Over time some parts of the dolomite had slowly been altered to flint. Flint is a rock where the host mineral, here dolomite, has slowly been replaced molecule by molecule by a microcrystalline quartz known as silica. Flint, chert, and jasper are all microcrystalline quartz rocks that are produced in similar ways. The naming differences are often subjective to the uses for the particular rock where rocks with known archeological significance are called flints, as in this instance. 

The source of the silica for the flint is partially a mystery though. There are several hypotheses for where it could have come from. One theory is that an eruption from the Yellowstone supervolcano dropped ash in the area 675,000 years ago. Ash is predominantly silica (quartz) and has been found in several areas of the park in beds up to three feet thick. It is also possible silica was brought in during deposition of the overlying Ogallala Formation which brought in sediment from the Rocky Mountains of Colorado and New Mexico around 10 million years ago. And a third theory is that immediately after the formation of the dolomite, the dolomite was then replaced by the silica nearly instantaneously in a geological sense. 

The quality of the flint is heavily dependent on the size of the quartz crystals. While in modern day, large quartz crystals may be more visually appealing, large crystals were considered "garbage" and were thrown away by Indigenous people because it reduced the effectiveness of the flint as a cutting tool. Larger crystals were produced along cracks of the dolomite, similar to a geode, where the space allows the crystal to grow with the groundwater. The finer the quartz crystals, the sharper the edge that was possible in the flint. Flint pits, as is seen here, were dug up to try and harvest the fresh flint that had not been weathered. 

References
at No comments:
Labels: ,

Tuesday, November 14, 2023

Geology through Literature - Walden




Using Walden by Henry David Thoreau

Science is not a new invention. People have been performing science for many thousands of years. Often they build on the research of those before them and sometimes they start from scratch. The purpose of this project is to use a scientific study from the 19th century to produce a current contour map of lake depth.

The study being described is in Walden by Henry David Thoreau, written before 1854. The book is typically considered “philosophical” literature but in this case he performs the basis of science. He identified a problem, determined how to solve the problem, and then executed the research. Below are a series of assignment questions and directions, however I have also included my answers and some additional information. There is a link at the bottom to the assignment itself without the answers intermingled. 

His Problem:
Often people would describe the depth of Walden Pond as bottomless. He wished to prove them wrong and determine the actual depth.

His Method
 To determine the actual depth of the lake he used the simple method of a rock and string.

His Solution:
That’s where you come in.

Project Directions
1. Read the “The Pond in Winter” chapter of Walden by Thoreau. For reference the important excerpts from the chapter are provided here:
"As I was desirous to recover the long lost bottom of Walden Pond, I surveyed it carefully, before the ice broke up, early in '46, with compass and chain and sounding line. There have been many stories told about the bottom, or rather no bottom, of this pond, which certainly had no foundation for themselves.... Many believed that Walden reached quite through to the other side of the globe.... But I can assure my readers that Walden has a reasonably tight bottom at a not unreasonable, though at an unusual, depth. I fathomed it easily with a cod-line and a stone weighing about a pound and a half, and could tell accurately when the stone left the bottom, by having to pull so much harder before the water got underneath to help me. The greatest depth was exactly one hundred and two feet; to which may be added the five feet which it has risen since, making one hundred and seven feet." 
"...this one, which is so unusually deep for its area, appears in a vertical section through its centre not deeper than a shallow plate." 
"As I sounded through the ice I could determine the shape of the bottom with greater accuracy than is possible in surveying harbors which do not freeze over, and I was surprised at its general regularity. In the deepest part there are several acres more level than almost any field which is exposed to the sun, wind, and plow. In one instance, on a line arbitrarily chosen, the depth did not vary more than one foot in thirty rods; and generally, near the middle, I could calculate the variation for each one hundred feet in any direction beforehand within three or hour inches." 
"... Having noticed that the number indicating the greatest depth was apparently in the centre of the map, I laid a rule on the map lengthwise, and then breadthwise, and found, to my surprise, that the line of greatest length intersected the line of greatest breadth exactly at the point of greatest depth, notwithstanding that the middle is so nearly level, the outline of the pond far from regular, and the extreme length and breadth were got by measuring into the coves...." 
"Of five coves, three, or all which had been sounded, were observed to have a bar quite across their mouths and deeper water within, so that the bay tended to be an expansion of water within the land not only horizontally but vertically, and to for a basin or independent pond, the direction of the two capes showing the course of the bar.... In proportion as the mouth of the cove was wider compared with its length, the water over the bar was deeper compared with that in the basin."

2. Write down all important sentences and phrases that have to do with the depth and shape of the pond.

3. Summarize these into only the important points (like the location and depth of the deepest point).
  • The deepest point of the lake is 102-107 feet deep and is located at the intersection of the greatest breadth and the greatest width lines.
  • There are sandbars that surround the coves creating mini lakes.
  • The pond is regular, meaning that the contours are evenly spaced apart.
  • The base of the pond is relatively flat.
4. Use one of the outlines of Walden Pond provided to start and outline the important features (deepest point, sand bars, etc.) in pencil.

In order to provide a map that is usable for this exercise, I first took an aerial image of Walden Pond. 


This was then traced and the aerial image was removed with the approximate location of Thoreau's cabin added for context.

5. Make a contour depth map (bathymetric map) with 20ft contours. The shore of the lake will be your 0 contour (provided). Then erase all of the mistakes and non-important items on the map so you just have a finalized contour map left.

Following these directions, as well as directions on how to make a contour (bathymetric) map, people should be able to make a fairly accurate Walden Pond bathymetry map.




And then students can compare their results with a professional map result called Hydrology and Trophic Ecology of Walden Pond, Concord, Massachusetts by Paul J. Friesz and John A. Colman, 2001 seen below:



You can also get a zip file with a complete set of directions as well as a step by step solution over at my site - http://www.dinojim.com/Geology/GeoEducation/GeologyThroughLiterature.html. 
at No comments:
Labels:

Monday, November 13, 2023

Geology of the National Parks in Pictures - Independence National Historical Park

My next post about the Geology of the National Parks Through Pictures is from when we lived in Buffalo, NY and were touring possible residency programs for the wife.  

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

-----------------------------------------------------------------------------


Driving to the locations of possible residency programs for the wife we ended up touring Philadelphia and the sites of Independence NHP. This is one of those parks where at first glance there are very limited geology around however there's always geology to be found. 

One of the most important buildings in United States history, the Pennsylvania State House, more commonly known as Independence Hall today. It was built between 1732 and 1748 primarily of brick and wood. However, there are some more geologically related pieces in the construction. 

Between the first and second story windows are a series of stone panels. The source of these panels seems to be from an abandoned "marble" quarry from Conshohocken, PA known as Potts' Quarry. The stone itself has many names, mostly because people at the time would call a building stone different names depending on the quarry from which it originated and not necessarily the formations where it came from. These rocks were known as "King of Prussia marble,” “Conshohocken blue,” “Schuylkill gray”, and "Pennsylvania Clouded Limestone". The clouded limestone seems to be the most prevalent name because of the description of the rock, calling the rock "clouded" or white. 

The rock is also not a marble at all, but a limestone. Although the chemistry would be similar, marble is a metamorphosed variety of limestone where the limestone underwent increased heat and pressure. This increase in heat and pressure would eliminate many things about the original limestone including any fossils and original sedimentary structures that would have been found in the rock. Pennsylvania Clouded Limestone is also not the geological term for the rock, however there isn't much I can find that ties this stone back to the original geology. From what I can tell the Pennsylvania Clouded Limestone found at the Potts' Quarry is from the Conestoga formation, a Middle Cambrian to Early Ordovician age deposit which has an abundance of limestone beds within it. 

The limestone panels can easily be seen behind the statue of Washington, which also happens to stand on a granite and marble base. The source of the stone I can not find but it comes from the Richmond Granite Co. This bronze version of the Washington statue was a replacement for the original Washington statue, which was made of Italian marble, and moved in 1910 to preserve it to Conversation Hall, on the second floor of Philadelphia's City Hall. 

The back, or south, side of Independence Hall boasts a statue of Commadore John Barry standing atop a piece of granite from the Harrison Granite Co. of Barre, VT. This is most likely a Devonian age granite:
"The Barre granite quarries expose a three-dimensional view of a small, well-studied pluton of the New Hampshire Plutonic Series. It is a Devonian talc-alkaline pluton formed by partial melting of Siluro-Devonian sedimentary rocks that had been folded and regionally metamorphosed during the Acadian orogeny and thus illustrates that the orogeny occurred rather suddenly in the region." (Richter, 1987)

Carpenter's Hall (seen here) does not have much geological context, however the Second Bank of the United States (which unfortunately I do not have pictures of) and is located generally between Independence Hall and Carpenter's Hall has Ordovician fossils in the floor panels. It had been determined that based on the fossils, the floor panels were derived from Isle La Motte Fisk Quarry which excavated the Crown Point Formation in Vermont. The quarry is now a part of the Chazy Fossil Reef National Natural Landmark. Identifiable fossils include gastropods, crinoids, corals, and cephalopods.

This is the Tomb of the Unknown Soldier of the American Revolution located in Washington Square, also a part of the national park. The wall behind the statue of George Washington is made of Indiana Limestone. The "Indiana Limestone" as it is officially called is likely the Salem Limestone, a Middle Mississippian age (335-340 million year old) light-grey to bluish-grey pure calcarenite limestone that crops out between Bloomington and Bedford in the south-central portion of Indiana. It is also the State Rock of Indiana. 

In front of the statue and the wall is a marble sarcophagus that hold the remains of an unknown Revolutionary War Soldier. The square itself is set upon a mass of "... unmarked graves within this square lie thousands of unknown soldiers of Washington's Army who died of wounds and sickness during the Revolutionary War." One of those graves was dug up, the remains determined to be that of a soldier and that soldier placed within the sarcophagus. I am unable to determine the source of the marble however, or even verify if the sarcophagus is actually made of marble and not granite. 


Another of the famous United States objects is the Liberty Bell. While not directly geological there is a geological story associated with the bell. Back in 1811, the New Madrid Fault, located along the western border of Tennessee produced one of the largest earthquakes along the eastern half of North America. The magnitude 7.2 earthquake is reported to have cause bells to ring all the way to Boston including the Liberty Bell in Philadelphia. 

Earthquake impact of the December 1811 New Madrid Fault. Image courtesy of Perdue University. 

Earthquakes in the east coast are often felt as far greater distances than those along the western coast of North America. This is because the rocks are older and the individuals faults within the older rocks have had time to heal. While in the west coast, since the area is still undergoing active deformation, the many faults located across the west absorb the seismic activity from the various earthquakes that are constantly occurring. This is why an earthquake which occur nearly 1,000 miles away from Philadelphia was able to be felt while in the western states it would be nearly unheard of to feel an earthquake that far away.  

References
at No comments:
Labels: ,
Subscribe to: Posts (Atom)