Ringer Park in Allston

Near Ringer Park in Allston you can see examples of sedimentary rocks (with volcanic rocks sitting on top). What about this formation tells you that these rocks are probably sedimentary? Look carefully at the next three pictures to answer the question.

Look at the layers of sandtone and mudstone below. Notice that there are bands of white rock running vertically through the dark rocks. These are known as veins. Which do you think formed first - the white veins or the sandstone and mudstone layers? What's your evidence?

It should be noted that the vein is not just on the surface, but goes deep into the rock itself. (Think 3-dimensional.)

In the picture below, you'll notice two rather large trees that seem to be growing right out of the rock. How is this possible? Look again at the pictures above.

Remember that in order for a tree or other plant to grow, it has to have soil, sunlight and water, and a place for the seed to land and germinate. Clearly the rocks formed millions of years ago, and the seeds appeared less than a hundred years ago!

Which layer - mudstone or sandstone - do you think the seeds started to grow in? From what you may have learned about these two types of rock, which would break down faster into soil, allowing for seeds to grow?

In the picture below, notice the contact between the sedimentary rocks (on the bottom left) and the volcanics (on the upper right).

Notice that the layers of sedimentary rock are almost horizontal. Yet, the volcanics seem to have formed in a way that cuts through the layers of rock. How do you think this happened?

To see a larger, labeled picture, click on the picture below.


Matching Game!

The three pictures below show three different rocks formed under very different conditions. Yet their appearance is similar.

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

A. 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 a hard, dense rock.

B. Small chunks of rock are ejected during a volcanic eruption. These chunks are deposited in fine-grained volcanic ash. The whole mixture gets cemented together.

C. Flowing Lava has small gas bubbles in it. As the lava cools rapidly, these bubbles are trapped. These bubbles fill with minerals as the lava cools.

Rock 1 (picture is about 2 feet across)

Rock 2 (picture is about 2 feet across)

Rock 3 (picture is about 4 inches across)


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