One can test the hypothesis that 'differential erosion' is a significant factor in shaping the details of landscape in the areas discussed above by comparing land surface elevation to the character of the underlying bedrock. This may be done using the following procedure. 1. 2. Examine the topographic profile X-Y shown in Figure 7, above. The location of this profile is indicated in Figures 3 and 5. Create a geologic cross section by placing the edge of a blank piece of paper along line X-Y in Figure 5. Carefully mark the locations of the end of the line (points X and Y) on the edge of the paper. Now draw strips of black on the edge of the paper to indicate the locations of all bedrock that is relatively resistant to erosion (all patterns on the map except the New Jersey "Redbeds" and the Inwood Formation). Next, take the marked edge of the paper and place it along the topographic profile X-Y in Figure 7. Wherever there is a resistant rock present, make a vertical black stripe from the top to the bottom of the profile. Do the ridges and valleys on the topographic profile coincide, respectively, with the black and white sections along the geologic cross section? Yes No Is the hypothesis of differential erosion confirmed or negated? (Circle One) Confirmed

Applications and Investigations in Earth Science (9th Edition)

9th Edition

ISBN:9780134746241

Author:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa

Publisher:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa

Chapter1: The Study Of Minerals

Section: Chapter Questions

Problem 1LR

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Transcribed Image Text:One can test the hypothesis that 'differential erosion' is a significant factor in shaping the details of landscape in the areas discussed above by comparing land surface elevation to the character of the underlying bedrock. This may be done using the following procedure. 1. 2. Examine the topographic profile X-Y shown in Figure 7, above. The location of this profile is indicated in Figures 3 and 5. Create a geologic cross section by placing the edge of a blank piece of paper along line X-Y in Figure 5. Carefully mark the locations of the end of the line (points X and Y) on the edge of the paper. Now draw strips of black on the edge of the paper to indicate the locations of all bedrock that is relatively resistant to erosion (all patterns on the map except the New Jersey "Redbeds" and the Inwood Formation). Next, take the marked edge of the paper and place it along the topographic profile X-Y in Figure 7. Wherever there is a resistant rock present, make a vertical black stripe from the top to the bottom of the profile. J Do the ridges and valleys on the topographic profile coincide, respectively, with the black and white sections along the geologic cross section? Yes No Is the hypothesis of differential erosion confirmed or negated? BEDROCK III diabase E sandstone & shale Actually, the rock formations underlying profile X-Y are not vertical layers. As diagrammed in figure 8, below, they vary from inclined planar beds west of the Hudson River to highly contorted beds underlying Manhattan and the Bronx. schist ENT marble gneiss ISADES HUDSON ANTON (Circle One) MANHATTAN 127 B Confirmed ZUARLEN C VO [*** FIGURE 8. Block diagram showing the topography and bedrock geology of northern Manhattan, the western Bronx, and the Palisades of adjacent New Jersey.

Transcribed Image Text:The Palisades As seen above, an explanation for the topography of Manhattan and the Bronx may be found in variable resistance of bedrock to erosion. A similar control of landscape by variable resistance of bedrock has been proposed for the west bank of the Hudson River. This control is called "differential erosion." There, the Palisades is an elongate ridge that parallels the shore of the river. The east side of the ridge is a sheer cliff that rises hundreds of feet. The west side of the ridge slopes gently downward to the west. The topographic profile X-Y, shown in Figure 7 below, illustrates the asymmetric character of the Palisades ridge and also shows details of the topography of northern Manhattan and the South Bronx X X X X a SAMPLE 4 5 6 7 b Hudson Harlem River River In figure 7, the locations of the Hudson and Harlem Rivers are shown. Which letter (a, b or c) indicates the position along the profile of the following three other important features: The ridge of northern Manhattan The Palisades ridge The ridges and valleys of the southern Bronx Topographic Profile X-Y FIGURE 7. Topographic profile along X-Y from Figures 3 and 5. SCRATCH TEST (NAIL) Igneous Igneous Sedimentary Sedimentary Is sample 6 more or less resistant than samples 4 and 5? Is sample 7 more or less resistant than samples 4 and 5? B Rock samples 4 and 5 were taken from the Palisades. Rock samples 6 and 7 represent the rocks that occur to the west of the Palisades and are also found in the narrow strip of low land between the foot of the Palisades cliff and the waters of the Hudson River. Test the resistance to erosion of these four samples (i.e., test them with the nail and the acid.) 126 65 A Co Y ACID TEST Less Less

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