. The Andes of southern Peru; geographical reconnaissance along the seventy-third meridian. Yale Peruvian Expedition (1911); Physical geography; Geology. PHYSIOGRAPHIC AND GEOLOGIC DEVELOPMENT 237 be referred to the early Palaeozoic, while some of them may date from the Proteriozoic. The Silurian beds are composed of shale, sandstone, shaly sandstone, limestone, and slate with some slaty schist, among which the shales are predominent and the limestones least impor- tant. Near their contact with the granite the slate series is com- posed of alternating beds of sandstone and shale arranged in be
. The Andes of southern Peru; geographical reconnaissance along the seventy-third meridian. Yale Peruvian Expedition (1911); Physical geography; Geology. PHYSIOGRAPHIC AND GEOLOGIC DEVELOPMENT 237 be referred to the early Palaeozoic, while some of them may date from the Proteriozoic. The Silurian beds are composed of shale, sandstone, shaly sandstone, limestone, and slate with some slaty schist, among which the shales are predominent and the limestones least impor- tant. Near their contact with the granite the slate series is com- posed of alternating beds of sandstone and shale arranged in beds from one to three feet thick. At Santa Ana they become. E3 Granite Schist SlSandstone Basalt Porphyry Fig. 158—Geologic sketch map of the lower Urubamba Valley. A single traverse was made along the valley, hence the boundaries are not accurate in detail. They were sketched in along a few lateral traverses and also inferred from the topography. The country rock is schist and the granite intruded in it is an arm of the main granite mass that constitutes the axis of the Cordillera Vilcapampa. The structure and to some degree the extent of the sandstone on the left are represented in Figs. 141 and 142. more fissile and slaty in character and in several places are quar- ried and used for roofing. At Eosalina they consist of almost uniform beds of shale so soft and so minutely and thoroughly jointed as to weather easily. Under prolonged erosion they have, therefore, given rise to a well-rounded and soft-featured land- scape. Farther down the Urubamba Valley they again take on the character of alternating beds of sandstone and shale from a few feet to fifteen and more feet thick. In places the metamor- phism of the series has been carried further—the shales have be- come slates and the sandstones have been altered to extremely re- sistant quartzites. The result is again clearly shown in the topog- raphy of the valley wall which becomes bold, inclosing the river. Please note tha
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Keywords: ., bookauthorbo, bookcentury1900, bookdecade1910, booksubjectgeology
