The two pictures below show layers of Roxbury Conglomerate and Sandstone (and possibly some mudstone as well). Can you spot where the different rock types are in these pictures? Don't let the rock wall on top confuse you!

Look carefully at the next four pictures.

What kinds of conditions do you think the different rock types formed in? Draw or describe the places where the sediments were deposited that eventually cemented together to form rock.

The sediments that formed these rocks were all deposited in the same location, but at different times. What do these rocks tell you about changes in the environment, in this location, over time?

NOTE: The green color on these rocks is due to lichen, not part of the rock. Don't let that confuse you!

In the three pictures below, notice that the layers in the sandstone are not completely horizontal. They most likely were deposited horizontally, but something happened after the layers of sand were deposited. What processes would cause this to occur?

NOTE: The green color on these rocks is due to lichen, not part of the rock. Don't let that confuse you!

Matching Game!

Try to match the rock with the description of how it was formed.

A. Pebbles, boulders, sand and mud are scraped up by the movement of glaciers. This "glacial till" gets deposited somewhere. Over time the rocks and sand get cemented together to form rock.

B. Pebbles and small boulders are deposited, along with sand, at the bottom of a shallow waterway. Over time the rocks and sand get cemented together to form rock.

C. Sand is deposited at the bottom of a deep waterway. Over time the rocks and sand get cemented together to form rock.

Need the answers? Click here

Hidden in the woods, behind Bloomingdale's at the Chestnut Hill Mall (near the bus stop), is a flat outcropping of rock. This rock happens to be Roxbury Conglomerate, although it has been so smoothed out that it's hard to see the rock type in the pictures. (The second picture is a zoomed-in copy of the first.)

You'll notice that the surface has two sets of scratches almost perpendicular to each other. Both of these sets of scratches were caused by glaciers as they advanced South. (We call this "glacial scarring".) It is uncommon to find two sets of scratches, since the later glacial event generally wipes out the earlier one.

But wait! How is it possible for two sets of glacial scratches (one earlier than the other) to both be oriented south, if they are perpendicular?? What could have happened here? Hint: think about the difference between the entire ice sheet moving and what individual, much smaller, parts of it might have done.

Can you tell which set of scratches is older? What is your evidence?