We could draw such a profile across several miles of landscape so we would see a side-view of the land's surface over which we might be hiking.For example, we could use a ruler to draw a straight line (a "transect") from the northwest corner to the southeast corner of the topographic map in our lab kit; then we could draw in the topographic profile along this transect by using the contour line information on the map (as done on page 18).In the next lab, we will learn how to use local geologic information from outcrops to begin to build such regional geologic maps and geologic cross-sections, but for now we just want to practice how to read them.Remember when we drew a topographic profile for lab manual exercise #1 (page 18) on Topographic Maps?Question 2: What is the sequence of events that can be inferred from the above cross-section?The two intrusions are labeled as X and Z; the surrounding rock (called the "country rock") is labeled as D.
What principle(s) of relative dating did you use in order to arrive at your interpretation of the relative timing of each event?
When did all this faulting take place (that is, between the times of which two sedimentary layers did the faulting occur)? Notice the "Great Angular Unconformity" shown on the North Half of the profile.
This is not labeled as such -- but see how the rocks at the bottom of the profile have been tilted while the younger rocks on top are horizontal.
We have seen that a cliff or a road cut is a local "geologic cross-section" -- a side view of the geology at one location.
As geologists piece together the information at various outcrops, they can begin to assemble a "geologic map" (like a road map) of an entire region (consisting of many square miles).
In the same way, such a transect could also show the inferred profile of the geology underfoot -- the expected rock layers and structures beneath the land from the northwest corner to the southeast corner of the map. You can open a larger version of this diagram by clicking on it.