These sections are typical of the ones geologists prepare when studying the relationships of layers of rocks (beds) throughout a region. Each column represents the sequence of beds at a specific locality. The same beds, which in places may thicken or thin (some may pinch out entirely) according to the local environment of deposition, are bracketed within the lines connecting the three columns.

From http://pubs.usgs.gov/

 

Now correlate your own rock layers in the activity attached to this page. Submit your completed activity to the dropbox.