Relative dating practice
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.
Notice that the various sedimentary layers have been labeled with letters.
Click Question 1: What is the sequence of events that can be inferred from the above cross-section?
What principle(s) of relative dating did you use in order to arrive at your interpretation of the relative timing of each event?
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.
Notice that the rock layers are each labeled with several letters.
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).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.This map displays the large-scale (also called "regional") geologic features they have inferred are present beneath the landscape.Along with these geologic maps, we can reconstruct a regional geologic cross-section which would be like a great "geologic slice" through the landscape.