Activity 5.8G Geologic History of Southeastern Pennsylvania Name: Course/Section

Question

Activity 5.8G Geologic History of Southeastern Pennsylvania Name: Course/Section: Date: Review Fig. 5.19. Then study the portion of a geologic map of Pennsylvania in Fig. A5.8.1. The green-colored areas are expo sures of 200-220 million-year-old Mesozoic sand and mud that were deposited in lakes, streams, and fields of a long, narrow valley. The red-colored areas are bodies of basalt about 190 million years old. Paleozoic and Precambrian rocks are more than 252 million years old and colored pale brown. +Ithaca STUDY AREA 0 5 10 15 20km 0 10 miles Washington Paleozoic rocks Reading Mesozoic- Rocks Mesozoic sedimentary rocks Pottstown . rocks Figure A5.8.1 Based on their geometries (as viewed from above in map view), what kind of igneous bodies on the map are labeled A? Based on their geometries (as viewed from above in map view), what kind of gncons bodies on the map are iabeled B (more than one answer is possible)? C REFLECT & DISCUSS If you could have seen the landscape that existed in this part of Pennsylvania about 200 million years ago (when the bodies of igneous rock were lava), what else would you have seen on the landscape besides valleys, streams, lakes, and fields? Explain your reasoning.

Explanation / Answer

A)The igneous bodies seem to cut across the sedimentary rocks perpendicularly.This is a typical property of intrusive bodies called dykes.

B)The intrusive bodies parallel to the sedimentary rocks are known as sills.

C)The presence of a sedimentary environment suggest high mountains of palaeozoic or Precambrian rocks; possibly residual in nature(no evidence of tectonism is present)

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