Bulletin of the Geological Society of America (1911) (20449826155)

Title: Bulletin of the Geological Society of America

Identifier: bulletinofgeolo221911geol (find matches)

Year: 1890 (1890s)

Authors: Geological Society of America

Subjects: Geology

Publisher: (New York : The Society)

Contributing Library: Smithsonian Libraries

Digitizing Sponsor: Biodiversity Heritage Library

Text Appearing Before Image:

EXAMPLE OP A EAULT SYSTEM 169

Text Appearing After Image:

ing metamorphosed the underlying conglomerate it is also in relief, can be easily identified and its outcrops followed. Conditions for study could hardly be more ideal. The complex mosaic produced by the faults is well brought out by the out- crops of both basalt layers (see figures 39 and 40). Blocks which are repre- sented on a small scale in figure 40 are, however, each subdivided into many blocks of lower order. Thus the cliff represented at a a (figure 40) when studied in detail reveals the complex system of faults which is represented in figure 41, and much the same could be said of each ^^^gurv: 39. section of the district. A The arrangement of these fragments of a thin flow particularly ragged group of basalt having a flat easterly dip was caused by an of fault blocks outlined in elaborate system of faults. South Britain, Connec- - T, , n ,1 ,1 ticut (U. S. Geological Survey). baaalt toward the north end of the basin has acquired the appropriate name of "Eagland." The appearance here and in the near-by Orenaug Hills the writer has likened to a jam of floating ice-cakes. Along the course of a graben-like canyon, between the last mentioned hills, the fault blocks are well displayed and have been described in the following words (see figure 42) : "In crossing the west twin of Orenaug Hill in a direction from west to east, one encounters cliffs nearly at right angles to the course which are too steep to be sealed. From the top of these cliffs the rock surface, with its thin layer of mold, inclines gently to the eastward to the foot of a similar cliff, to which succeeds a gently sloping summit and a new cliff", as before. Approaching the eastern margin, cliffs appear upon the east, and these soon become the most important ones. If next a start be made at the northernmost point of the basalt in the same hill, where it terminates in a sharp prow between steep cliffs on both the east and west, . . . and a course be taken southward through the intermontane valley, the nearly vertical eastern cliff face, which trends south ± 5 degrees east, can be followed on the right over a quarter of a mile for a portion of the distance in a narrow canyon. After emerging from the canyon the cliff recedes on the right, but its direction is continued in a cliff on -Effect of Faults in displacing a Basalt Flow

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1911

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