The rocks of the Mohawk and Hudson Valleys of upstate New York tell a fascinating story, both through the rock layers themselves, as well as the life contained within them. Each individual outcrop, while interesting in many ways, pales in comparison to the story that unfolds when many of the units are compared and contrasted regionally. What comes to the surface is a story of tropical seas, violent mountain-building and active volcanoes. Read a bit about the background geology of the region, or go to the bottom of the page to begin your journey.

Above is a map of New York State. The area in purple marks the counties where this portion of our field trip will be conducted.

This is an introduction to those that may not be entirely familiar with the geologic timescale. Should you need to, you will be able to access this table througout the fieldtrip.

Most of this field trip centers on rocks of Cambrian, Ordovician, Silurian and Devonian age.

As an introduction, the basic events affecting the types of rocks we will see in this fieldtrip (in order)

1. Cambrian: A shallow sea in the interior of North America, ideal for carbonate deposition (limestone and dolostone).

2. mid-Ordovician: small pieces of land (island-arc) approaching ancient North America. The fact that two landmasses are converging creates a downward warp to the west in the interior of North America. This is known as a foreland basin.

3. mid-Ordovician: As a result of this basin being formed, deopisition occurs within it. The closer to the collision, the more muds and coarser-grained particles that are being shed from the east, producing shales, siltstones and sandstones. The further away from the collision, the more limestone is produced.

4. late-Ordovician: Collision occurs, producing major thrust faulting, as the elements of the island arc (allochthon - defined as "A rock that has been moved a long distance from its place of origin.") are thrust up and over the North American autochthon. Mountains form and are eroded.

5. late-Silurian: Quiet, shallow seas, ideal for the deposition of limestones and dolostones.

6. Devonian: More mountain building and thrusting of rock layers as Europe collides with North America, forming the continent of Laurentia. Rocks laid down during late-Silurian and early-Devonian times, as well as rocks deposited earlier, are tilted and faulted.

Of course, this is an an extremely over-simplified account....almost embarrassingly so. It is intended as a jumping-off point for those with no knowledge of the rocks of east-central New York State.

At any time during this fieldtrip, you can go to the top of any page and click on this symbol:
A separate browser window will pop up. By matching the number in the upper left-hand corner of every photo with this location map, this will allow you to see where each photograph was taken.



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This field trip was created around an actual field trip lead by Dr. Carlton Brett of the University of Cincinnati from June 30 through July 2, 2000, along the Mohawk River and Hudson River valleys of New York State. I would like to thank Carl, along with Gordon Baird, Professor of Geology at SUNY-Fredonia, Ed Landing, State Paleontologist at the New York State Museum, and all of Carl's students (both graduate and undegraduate) who provided much of the geologic information to make these pages possible.


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