Note 6 — THE ROCKS OF CALVIN COOLIDGE STATE FOREST PARK AND THE STORY THEY TELL

The geologist divides geologic time into four major sections, designated Eras. These Eras are in turn subdivided into Geologic Periods which are of shorter time duration. The Cambrian Period is the oldest of the Paleozoic Era and began some 550 million years ago. The Ordovician Period is the next oldest of the Paleozoic Era and started about 440 million years ago and ended close to 360 million years ago.