The Quarterly journal of the Geological Society of London . he sameexposure, there are yet certain characteristics which are common tothe whole of them. Essentially, these crush-conglomerates are rocksmade up of scattered fragments set in a slaty matrix. The fragments vary in composition, but most frequently are com-posed of fine-grained grit or sandstone, and of sandy slate ; with lessabundant pieces of coarsish grit, of banded flaggy slate, and of purelyargillaceous smooth blue slate or shale. These fragments areusually phacoidal or lenticular in outline,1 but the shape differs indifferent s
The Quarterly journal of the Geological Society of London . he sameexposure, there are yet certain characteristics which are common tothe whole of them. Essentially, these crush-conglomerates are rocksmade up of scattered fragments set in a slaty matrix. The fragments vary in composition, but most frequently are com-posed of fine-grained grit or sandstone, and of sandy slate ; with lessabundant pieces of coarsish grit, of banded flaggy slate, and of purelyargillaceous smooth blue slate or shale. These fragments areusually phacoidal or lenticular in outline,1 but the shape differs indifferent sections, and also according to the size. In some localitiesmany of the smaller inclusions are quite rounded, while in othersthey take the form of subangular or spindle-shaped strips (seefigs. 7 and 8, p. 572). The fragments are of all sizes, from blocksseveral feet in diameter (see fig. 1) to particles of microscopic Tig. 1.—Crag at the southern edge of Gronk SumarTc, Sulby.(Shoiving large block of coarsish-grained grit in crush-con-glomerate.) W. 20. S. A. Block of sheared, slightly felspathic grit, about 8 feet long, embedded with many fragments of fine-grained flagstone and hard clay-slate in a matrixof bluish slaty material. B. Inclusions in which the original bedding is still visible. The arrow indicates the probable direction of the shearing. dimensions. They are, as a rule, indiscriminately mingled, large andsmall, in a highly-sheared slaty matrix; but the average size of theinclusions varies greatly in different localities, and there is some-times a total absence of the larger fragments. A glossy sericitic face, evidently the result of shearing, coats theharder inclusions; and planes of similar character are abundantthroughout the matrix, and sometimes cut the fragments. Theseschistose planes determine the weathering and the fracture of the 1 Such fragments often appear nearly circular when cut across at right anglesto their longer axis. Vol. 51.] CRUSH-CONGLO
Size: 2371px × 1054px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1840, bookidquarte, booksubjectgeology
