Homework #5     Due on Friday, March 6, 1998.

Sedimentary Rock Description

Instructions:  Go to Bowman Hall (corner of Rose and Washington), to the Main Entrance on Washington St. (this entrance is the one with the big columns; you can't actually get into the building there, but it's still the main entrance).  Carefully examine the rock that is used to make up the stairs, the columns, and the lowest 4 feet of the building in this area.

1.  Sketch fossils.  Look carefully for fossils in this rock.  Look at many different blocks of the rock to find several good examples of fossils.  They are mostly quite small and broken into pieces.  You probably won't be sure what type of fossil you are seeing, but if it looks like an organized structure of some sort, and you can find more than one example of it, it probably is a fossil. If you have a magnifying glass, use it.
    Sketch at least 5 different examples of fossils you find, making sure that you represent at least two different types of fossils.  On each sketch, include a scale.  For example, if the fossil is only as big as this letter "O", try making your sketch significantly bigger and including a note that shows how big the actual fossil really was.  Carefully describe each fossil in a sentence or so.

2.  Evidence for currents.  Cross-bedding is found in several of the rocks on the steps.  The cross-bedding was apparently made by small ripples, only a few centimeters high.  On some of the beds, you can find the cross-bedding on the top of the bed instead of on the sides as it is shown in the book (see page 127).  What do you think cross-bedding might look like from the top?
     Find two examples of cross-bedding and sketch them, including a scale.  Explain why you think this is cross-bedding.  Find something in the rock that you think might be cross-bedding viewed from the top of a step, and sketch that too (a third sketch).  On some steps, you may be able to see both sides and top on the same block of rock.

3.  What kind of rock is this?  Where did it form?  How hard is this rock?  Try scratching it with your keys or a knife and then with a copper penny.  What mineral might make up the bulk of this rock?  What are fossils commonly made of?  Is this a chemical or detrital rock, do you think?  What is the average grain size?
     Describe and give a name for this rock, and explain carefully why you call it that.  Then explain what environment of deposition it might have formed in, long ago.  Explain why you suggest such an environment, including what evidence you use to support your interpretation.