File:The American journal of science (1902) (17964135608).jpg

Title: The American journal of science
Identifier: americanjourna4141902newh (find matches)
Year: 1880 (1880s)
Authors:
Subjects: Science
Publisher: New Haven : J. D. & E. S. Dana
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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400 FT. //. Hobhs—Instance of the Action of the agencies of subserial and of ice erosion, we may believe that it would have presented an irregular surface not unlike that of a mosaic from which a local area of the back had become dis- placed and the overlying blocks allowed to slide down by small amounts while still restrained by their friction upon their neighbors. The effect of subserial erosion has been to etch out the marginal areas of soft sandstone and leave the basalt prisms of the central area in strong relief like the image of a cameo. The basalt itself discloses no marks of the subserial erosion, for the reasons : first, that it is intensely resistant; and, second, that its area is so small (six miles in length by two miles in greatest breadth) that no streams of any power have been developed upon it. It is not, however, to be assumed that no considerable degradational action has occurred within the area of the basalt masses of the valley, for the three upper members of the Newark series found in the Connecticut Val- ley area, which begins less than a score of miles to the east, are missing from the Pomperaug Yalley series, and were doubtless removed by subserial erosion, while large thicknesses of the surrounding schists were being carried away.
Text Appearing After Image:
Fig. 1. Schematic profile of basalt ridges of the Pomperaug Yalley. Black, basalt; black spotted with white, amvgdaloidal basalt; white, shale : white with black circles, conglomerate (where stippled, baked zone of con- tact) ; stippled area, drift and alluvium. The work of the ice within the valley is revealed in the pro- files of the basalt ridges. These ridges have generally fault scarps on their western and northern sides (which face in the direction from which the ice moved) and gentle slopes to the eastward and southward, conforming to the dip of the beds and flows of which they are composed. In these general outlines the action of the ice is not disclosed, but the caps of all the ridges seem to have been removed by an appreciable fraction of their height. This is brought out in the schematic figure 1 and in the author's report above cited.^ That this degrada- tional action by the ice is localized largely at the crests of ridges is also shown by the texture of the rock found at the crests when compared with that upon the fianks of the southern ridges. Dense and massive at the crest in correspondence with the lower beds of the flow, it is amvgdaloidal and vesicu- lar upon the southeastern flanks, where it doubtless represents upper layers of the flow. * Loc. cit., pi. V, A.

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