New York State High School Regents Exam Prep
Earth Science

Ways to Correlate or Match Rock Layers (Strata)

Walking the outcrop done by following a layer of rock from one end of the outcrop to the other. If you can see the rock layer and touch it, then you can correlate it.

Comparing properties of the rock strata compare things such as color, texture or compsition. The most important property is the sequence of the rock layers.

Index fossils used to find the age of the rock in which it is found. The best index fossils are organisms that were around for a short time geologically, but were found over a large area of the earth.

Volcanic Ash Falls When a volcano erupts violently a layer of volcanic ash is spread over a large area. Such as Mt. St. Helens in Washington State. These ash falls are very rapid events, over a large area, which makes them a very reliable time marker

Test Your Knowledge


Use the geologic profile above to answer the following questions.
The diagrams represent two rock outcrops found several miles apart in New York State.
1. Which layers are the same?


2. Of the rock layers E and F, which is the oldest?


3. What is the correct sequence of rock layer from oldest to youngest?


4. An unconformity (buried erosional surface) is represented by the interface between which two layers?


5. What type of rock is layer A?


New York State High School Regents Exam Prep Center: Earth Science