. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. woodworth: geological expedition to hkazil chile. 73 indicate, by the detailed structure of the surfaces, that the down- throw was on the northeast side in accordance with the structure of the Orleans basin. It is evident therefore that repetitive small faults occasion the base of the Permian section in this district. The conglomerates are exposed along the river banks below the. ^^^ \y^r\y\^7<y Fig. 21.— Section of beds in Orleans basin, south bank of the Rio Tuberao. The rock on west is a broad trap
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. woodworth: geological expedition to hkazil chile. 73 indicate, by the detailed structure of the surfaces, that the down- throw was on the northeast side in accordance with the structure of the Orleans basin. It is evident therefore that repetitive small faults occasion the base of the Permian section in this district. The conglomerates are exposed along the river banks below the. ^^^ \y^r\y\^7<y Fig. 21.— Section of beds in Orleans basin, south bank of the Rio Tuberao. The rock on west is a broad trap dike. town and are best shown on the north bank under the railroad track, (Fig. 22). There is here a water laid conglomerate mainly of granite pebbles with a few quartzite and quartz pebbles. The conglomerate is overlain by cross-bedded grits, the cross-bedding dipping to the north and northwest as if deposited by currents of water flowing at least locally in that direction. The pebbles in the conglomerate bed, mostly three inches in diameter, sometimes attain five inches, and are embedded in a paste of granitic detritus. The subrounded shape of the pebbles indicates no distant journey and their lithological character betokens a derivation from the granitic terrane which immediately underlies the local Permian section. (See Plate 25.) Another exposure of the conglomerate about 90 meters (lown stream from the preceding exposure presents the cross-section of a north- south ridge of coarse pebbles enveloped in cross-bedded sandstones. In a layer of conglomerate varying from 0 to 60 cm. in thickness the cobbles attain a diameter of 20 cm. The ridge-like de- posit, so suggestive of a buried esker, is apparently continued across the river on the south bank of which there is a ridge-like exposure of conglomerate also covered by sandstones. A few yards east of the ridge on the north bank there is exposed a bed with rounded granite pebbles scattered through a sandstone matrix as »if
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Keywords: ., bookauthorha, bookcentury1800, bookdecade1860, booksubjectzoology
