Mineral Resources of the Nabesna-White River District, Alaska (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1910 edition. Excerpt: ...the Tonopah mining district, Nevada: Prof. Paper U. S. Geol. Survey No. 42, 1905, p. 275. Cross, Whitman, Trachyte on the island of Hawaii: Jou. Geology, vol. 12, 1904, p. 520. siderable local alteration has taken place, so that specimens from such localities closely resemble the Carboniferous amygdaloids of the White River country. Unaltered portions, however, consist of a fine-grained iron-gray basalt with large glassy porphyritic feldspars, which are notably tabular in habit. Many of the overlying lavas are similarly characterized by a conspicuous development of numerous large amber-colored labradorite feldspars. In the open country immediately north of White River there are a number of prominent mesas, which are capped by nearly horizontal flows of lavas. In that one locally known as Pingpong Mountain a columar structure is finely displayed above the cut banks of White River. The rocks of the mesas prove to belong to a number of varieties and types, gray porphyritic andesite, dark glassy hypersthene-augite andesite, and basalt being among those noted. Whether these lavas were erupted from the volcanic vents of the Wrangell Mountains is not known. It appears quite probable, from the fact that large andesitic dikes cut the underlying lignitiferous formation, that they may have been extruded from local conduits. QUATERNARY DEPOSITS AND GLACIATION. By Stephen R. Capps. DISTRIBUTION AND CHARACTER. The Quaternary deposits of this region are for the most part confined to the valleys of the larger streams. They consist of gravels and of bowlder clays, almost all of which are directly or indirectly due to glaciation. Glaciers have existed continuously from Pleistocene time to the present, and glaciofluvial deposition has been uninterrupted during this...