Monographs of the United States Geological Survey Volume 11

Monographs of the United States Geological Survey Volume 11

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1885 edition. Excerpt: Iceland, with the dust erupted in Java in 1864, and the similar material ejected in such quantities from Krakatoa in 1883, it is found to have the same physical characteristics; but it is much more homogeneous, and, unlike the greater part of the recent dust examined, is composed of colorless instead of brown or smoky glass. In the following figure, which we copy from STRATA OF VOLCANIC DUST. 147 Mr. J. S. Diner's instructive article on the volcanic sand which fell at Unalaska, October 20, 1883,49 the microscopic appearance of volcanic dust, from various localities and of widely different geologic age, is shown with accuracy. The peculiar concave edges and acute points of the shards of glass render it evident that they were formed by the violent explosion of the vesicles produced by the steam generated in the viscid magma from which the glass was formed, and were not produced by the mere attrition of the fragments during the process of eruption. It is noteworthy that the dust erupted from Krakatoa but yesterday is undistinguishable in its main characteristics from the material of a similar origin which fell in the waters of Lake Lahontan during the Quaternary, or from the dust thrown out by some unknown and long since extinct volcano in the vicinity of the Atlantic coast, which fell near the site of Boston during pre-Carboniferous or possibly in pre-Cambrian time. The volcanic phenomena of to-day are governed by the same laws as obtained at the dawn of geologic history. Farther study revealed that even the finest of the dust obtained from the basin of Lake Lahontan has identically the same physical properties as pumiceous rhyolite forming the Mono Craters, ground in a mortar to a corresponding fineness; under the microscope the more

Product details

  • Paperback
  • 189 x 246 x 6mm | 213g
  • United States
  • English
  • black & white illustrations
  • 1236991907
  • 9781236991904