Local and Western Maryland Geology

In Paint Branch, College Park, we observed a small stream. Around and in the stream were rocks of various sizes. Small sediments such as sand are carried by the stream because there is enough kinetic energy; however, there is not enough kinetic energy to move bigger sediments. Bigger sediments just sink to the bottom of the river when thrown in and are only capable of moving during a storm or flood. In areas where larger particle are located, the flow of water is slower than in the areas that contain smaller particles.

Two important things I learned about at this site were the cutbank, the region outside the stream curve, and the point-bar, the region inside the stream curve. The trees on the point-bar side were much younger than the trees on the cutbank because the point-bar is newer than the cutbank. As the cutbank gets eroded and replaces the river, the old river becomes the point bank. The materials on the point-bar came to their current condition by traveling from upstream the river. After the rocks get removed from the bedrock after erosion, the rocks get transported downstream. As the move down, the rocks hit against one another, making the rocks become smoother. Therefore, the rocks that are smoother can be assumed to have traveled the longest. The most abundant type of rock is quartz. Because it is much harder than other material, it is able to remain intact while being transported. Other materials such as sand stone disperse and break up quickly. The cutbank consists of mainly three different levels. The bottom layer consists of both solid material, which is clay, and pebble size material. The middle layer consists of gravel and sand, which later become part of the point-bar. It can be assumed that these layers had once extended to the point bar area but disappeared because of erosion because of the principle of lateral continuity. Also, the principle of superposition supports that the bottom layer was created first and so on.

There are changes in the level of the stream. Evidence of this is bunched up leaves far away from the stream; some leave are bundled up on one side of an object such as a plant or rock. In the future, the stream bed would not be in the same location if the same process continues. The stream bed would probably migrate towards the cut bank and make the old river a new point bar. From this, it is unreasonable to say that the Earth’s surface is permanent and unchanging. As can be seen from this example, the Earth’s surface is changing, creating new landscapes and features.

For our second stop, we went to a railroad cut in Western Maryland. The general sizes of the sedimentary grains in the rock were very fine. This implies that the area in which it was deposited was had very slow moving water such as a lake. The sediment consisted of only one mineral type: mudstone. The strata here were not horizontal but titled. The orientation was measure to be a strike of 32 degrees east and a dip of 28 degrees.

Along the same railroad, we stopped at another site. Here, the general sizes of the sedimentary grains were coarse; it consisted of sand. Compared to the previous site, the sediments were bigger. This tells us that the upland region had stream that flowed into a lake. The orientation of the beds here were tilted but not orientated as much.

The last stop along the railroad consThe last stop along the railroad consisted of igneous rocks. The intrusive igneous rocks showed no internal structures and were vertical. Relative to the sedimentary strata, the diabase is oriented at an angle. The sedimentary rocks came before the diabase because the diabase had conflicted with the sedimentary rock. There is no volcanic activity in Maryland today. The diabases shown currently in Maryland were formed long time ago. The diabases had been formed from the magma from volcanic acitivity.

Last modified: 17 November 2008