Welcome to the the Backbone of NYC Earth Cache that in this lesson talks about the oldest rock in NYC, Fordham Gneiss which along with schist and Inwood marble is one of the backbones of NYC. To get credit for this cache, you must Read the full lesson and understand it, go to the posted cordinants answer the 2 questions that are asked at the bottom of the description, and then post picture proof that you were there. Please do not post spoiler pictures of the answers, or your log will be deleted. Have fun!
Named for the Bronx neighborhood where it is most visible, Fordham gneiss was formed around 1.1 billion years ago, in the pre-Cambrian era, during a period of continental shifting. At that time, the continent of North America lay in a narrow basin beneath an ancient, shallow sea. Sand and silt had accumulated in the basin, forming sedimentary rock. During a continental shift, an unidentified landmass collided with North America, thrusting the sedimentary rock upward and forming a mountain range. This collision is known as the Grenville Orogeny, and it occurred at a time when life on earth consisted of algae and bacteria, and multi-celled organisms were beginning to evolve.
The impact of the collision and the high pressures involved caused the sedimentary rock to recrystallize, forming the black-and-white banded, metamorphic rock we see today. The contorted banding pattern of these bands is a testament to the immense geologic force of the shifting plates that formed the gneiss. Over the next hundred million years, passing glaciers and erosion by wind and water wore away the mountain ranges. Further shifting of the landmasses produced Manhattan schist, which can be observed at Inwood Hill Park’s Indian Houses; Inwood marble, named for this area where it can frequently be observed at the surface; and other bedrocks, which all came to rest on or beside the existing layer of gneiss.
till today Manhattan hosts some of the highest skyscrapers in the western world, like the 1,775 ft high Tower One of the new World Trade Center, completed in 2013. Tall buildings seem to be everywhere in New York, but a closer look reveals that they actually are clustered in two distinct areas: Downtown, the financial center, and Midtown - the home of famous landmarks like the Chrysler and the Empire State Building, built from 1930 to 1931.
The reason for the two distinct clusters is found in the geological history of New York. The island of Manhattan consists of three rock formations, known as Manhattan Schist, Inwood Marble and Fordham Gneiss.
These rocks are the remains of the collision of two enormous landmasses. Some 450 million ago, the collision of the baltic areas of modern Europe with northern parts of America formed the primordial continent of Laurussia. Laurussia eventually merged with Siberia and pushed south, colliding 300 million years ago with Gondwana, a landmass formed by the tectonic union of South America, Africa, Australia and Antarctica.
The collision of Laurussia and Gondwana closed an entire ocean, forming a new gigantic landmass named by geologists Pangaea. At this time present-day New York would have been very close to the supercontinent's centre, just where tectonic movements were forcing mountains upwards. The former mountains of New York probably achieved heights similar to what we see in the Himalayas today. Buried beneath 8 miles of growing mountains, marine sediments, like limestone and clay, were transformed over time by heat and intense pressure into metamorphic rocks, like marble, schist and gneiss. The metamorphic process also formed minerals like blue cyanite or red garnet, found today during excavation works in New York's underground.
Kyanite is a captivating mineral that often flies under the radar, yet it holds a treasure chest of intriguing facts. Known for its striking blue hues, kyanite is a metamorphic mineral found in aluminum-rich rocks. Its name comes from the Greek word "kyanos," meaning deep blue, which perfectly describes its vibrant color. But did you know that kyanite's hardness varies depending on its crystal axis? This unique trait makes it a favorite among geologists and gem enthusiasts alike. Beyond its beauty, kyanite is used in industrial applications, from ceramics to electronics. Its ability to withstand high temperatures makes it invaluable in manufacturing processes. Kyanite's metaphysical properties also attract those interested in crystal healing, believed to enhance communication and intuition. In some types of Fordham Gennis, you will see this mineral, or even red garnet. You may even find just regular quartz or even granet.
a) What is the geolodgical exposure? What colors and formations are in the rock?
b) How is the rock shaped? Is flat or tall, rough or smooth?
c) Identify the types of minerals you see in the rock? Tell me atleast one.