GEOS 112 -  Introduction to Earth Sciences

Making a Geologic Map
In this lab we will use our existing knowledge of rock types and map reading skills to make a geologic map of  parts of Trinity College's campus and surroundings.

Before you come to class:

Preparation for this Lab:
  • Read the information on geologic maps and the colors used to denote the different rock units.
  • Review the rock types you saw and described during last week's lab.
You should also take a look at this simplified geologic map of Connecticut.  Locate the position of Hartford on the map and check what rocks you might expect and how the information from the map works out with respect to your own personal notes.  For more information you can also check out the map in the geology lab.

What to bring:

We will meet in Front of Gallow's Hill Bookstore and spend the afternoon outside - rain or shine, so be sure to bring appropriate clothing.  We will also climb the cliffs along Summit Street, so make sure you are wearing sturdy shoes. Tennis shoes are OK, hiking boots are better.  Long pants will protect you from poison ivy, thorns and brush.  You will need:
  • your lab book and a bunch of pens (several colors would be good)
  • a base map of your mapping area (for a download click here), I will also bring a bunch of paper copies
  • compass
  • rock hammer
  • hand lens
Field Exercise:
With our help you will map the position of  rock outcrops found mostly along Zion Street.  When you find a rock outcrop you should note the following:
  • rock type (identify the rock using your notes from last week)
  • location of the outcrop:  chose a color for the rock type you are mapping and note its position on your base map
  • How far does the rock unit extend?  Where are its boundaries? 

The boundary between two rock units is called a contact.  When you find a contact make sure you:
  • enter its location onto your base map
  • draw the orientation of the contact onto your map.  You can use a compass to do this or you can orient yourself on the map and draw the contact freehand.

Once a certain pattern emerges you can connect the outcrops and contact information, mapping the distribution of rocks along the West side of campus.

In addition, measure the strike and dip of the rock units.  Note the location of your measurements on the map (you can number them or label them in any convenient way) and write the strike and dip measurements into your lab notebook.  By the end of this lab you should have a fairly neat table of several strike and dip measurements, listing the position of the measurement, the rock unit that was measured, and, of course the values for strike and dip.

The field version of your map should include:  All the sites where you identified rocks and contacts.  Your map should also indicate where you actually observed rock outcrops and where you simply infer the presence of a certain rock type.  It  should also include information about areas where rocks are hidden from view by buildings, or overlying sediment and soil.

For your lab notes make sure you include all the information we talked about last week.  This includes a short statement describing the purpose of this lab, the people who are working with you in a group, the weather etc.
Your final report should include:
  • A carefully drawn geologic map of the area investigated (use a new base map, use the proper colors and symbols, mark the location of your strike and dip measurements using the proper symbols).  Yes, every map needs a scale, North-arrow, legend etc..
  • Add the proper rock-units to the E-W profile of Trinity  College.  You can use your profile from last week or download a new version here.  Make sure you get the orientation of the rock units right as they disappear below the surface.  A profile that includes subsurface information is called a geologic crossection.
  • Include your field notes with your final map and crossection.
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