Geological History of Rochester

The geological history of the Rochester area is long, eventful, and very exciting to anyone curious about the mysteries of the planet's past recorded in rocks. This is but an attempt to briefly summarize the most outstanding events that shaped our landscapes, determined our energy, food, and mineral resources; events that occurred long before humans existed to witness their magnificent power. After all, "civilization exists by geologic consent, subject to change without notice".

(philosopher and historian Will Durant)

INTRODUCTION

Although this is written as a generalized history encompassing a large scope of geological events and avoiding extensive use of specialized vocabulary, it is still helpful to be familiar with the following key concepts, or frames of reference:

Geologic Time Scale:

For convenience, the Earth history is divided into four eras. The eras are subdivided into periods, which are further subdivided into epochs. This chart will be useful to the readers:
(from Bradford B. Van Diver Roadside Geology of New York; Mountain Press Publishing Company, fifth printing, 1992)

Plate Tectonics:

A theory that became one of the major building blocks of geological sciences in this century, plate tectonics states that crust and rigid upper mantle of the Earth behave as a unit called lithosphere. Lithosphere is divided into approximately 12 major plates, which ride on asthenosphere, a zone of greater plasticity. Tectonic plates can spread apart, ride past each other, or collide, producing ocean floors, causing seismic activity, and building mountain chains. Thus, there are times of continental togetherness, followed by times of continental drifting apart. These diagrams show the position of continents at different times in Earth history relative to each other.

Continents of the World

(from Bradford B. Van Diver, Roadside Geology of New York; Mountain Press Publishing Company, fifth edition, 1992)

Rock Cycle:

Rocks are divided into three major categories: igneous, sedimentary, and metamorphic.

In New York State, Cretaceous to Cambrian rocks are dominantly sedimentary; early Ordovician and Cambrian to late Proterozoic are metamorphosed; and middle Proterozoic (Helikian) rocks are intensely metamorphosed.
  • Overall Picture of Tectonic Past
  • Table of Contents