. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. WOODWORTH: geological expedition to AND CHILE. 131. , * X s ,⢠â ⢠⢠* f < ^V'cf::^ Malvoa Station, 79 kms., alt. 43 M. ( ft.). Good terrace on opposite or southwest side of river. At railway station there are clays. San Rosendo Station, So kms. alt. 46 M. ( ft.). East of the Station there was in 190S an excellent exposure of gravels and sands in a deep cut, rising about sixty-five feet above the railway, or to an elevation of 220 feet above sea-level. The annexed section is from a drawing made
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. WOODWORTH: geological expedition to AND CHILE. 131. , * X s ,⢠â ⢠⢠* f < ^V'cf::^ Malvoa Station, 79 kms., alt. 43 M. ( ft.). Good terrace on opposite or southwest side of river. At railway station there are clays. San Rosendo Station, So kms. alt. 46 M. ( ft.). East of the Station there was in 190S an excellent exposure of gravels and sands in a deep cut, rising about sixty-five feet above the railway, or to an elevation of 220 feet above sea-level. The annexed section is from a drawing made on the spot. (Fig. 37). This section reveals a succession of river deposits varying from sands like those now transported in this portion of its course by the Rio Bio Bio to coarse gravels including large boulders such as demand ice-rafts or the proximity upstream of glacial conditions. The lowest bed exposed (see Fig. 37) consists of dark sand with pebbles of a volcanic rock. Above this comes a coarse gravel including a boulder of gneiss about seven feet long. Next in the section is sand with thin bands of volcanic pebbles. Above these layers comes about twenty- five feet of dark sands with a thin band of volcanic pebbles. Surmounting this and forming the sur- face is a layer, about twenty-feet thick, of coarsely bedded gravels and boulders, the cross-bedding of which suggests the structure of a delta front. There are in this section thus the records of two episodes when the river transported to this point coarse gravels and boulders which it is to be presumed indicate con- temporary advances of the local glaciers or times of unusual melting and discharge of coarse debris. I saw no marine shells in any part of this terrace or on its surface, and no evidence of the presence of the sea in the deposition of the materials. The structure is quite like that of many glacial river deposits in the inland portions of glaciated North America. The lower bed of coarse gravel with b
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Keywords: ., bookauthorha, bookcentury1900, bookdecade1910, booksubjectzoology
