Question 3 (3 points): Finally, return to the list of hypothetical geologic examples and click on "two intrusions." Again, complete the sequence correctly and explain the logic and principle behind your choice for each event.
Let's return to one of the text questions we addressed as part of last week's homework.After the practice above, try a more thorough analysis of the history of the landscape shown on page 173 of our Chernicoff/Fox textbook.Notice that the various sedimentary layers have been labeled with letters.Also an igneous intrusion is present (labeled T) and a fault is present (labeled A).Remember when we drew a topographic profile for lab manual exercise #1 (page 18) on Topographic Maps?
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.
The two intrusions are labeled as X and Z; the surrounding rock (called the "country rock") is labeled as D.
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).
This map displays the large-scale (also called "regional") geologic features they have inferred are present beneath the landscape.
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).