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Analytical Abstracts of Current Literature.

Summary of Current Pre-Cambrian North American Literature.[note 1]

Cross[1] describes a series of hornblendic, micaceous and chloritic schists, on the eastern side of the Arkansas river, near Salida, Col. In places these grade into massive rocks. They are cut by granitic and pegmatitic veins, as well as by dykes of porphyry. A detailed microscopical study leads to the conclusion that the rocks are a metamorphosed volcanic series. The whole constitutes a part of a single anticline. The schists are unconformably below the Silurian, and as the known Cambrian in Colorado is a thin series of quartzites and shales conformable with the Silurian, the Salida schists are considered as pre-Cambrian. The relations of the schists to the Archean complex are not exposed, but they are probably a continuation of the hornblende-schists of Marshall Pass. Greenish schists are found at Tin Cup Pass, and near the town of Tin Cup is a highly crystalline marble interbedded with the green schists, and fine grained gneissoid rocks, showing that metamorphosed sedimentary rocks do exist among the crystalline schists of the Sawatch Range. Taking into account all the facts it is thought that the schists and massive rocks of the Salida section probably represent a great series of surface lavas, erupted in Algonkian time.

Smyth (C. H.)[2] describes the rocks near Gouverneur, New York, as consisting of gneiss, granite, limestone, and sandstone, with small amounts of associated schists. The gneiss is the oldest rock of the region, underlying the other formations. It sometimes grades into a true granite, the passage being gradual. The two are regarded as different phases of the same rock, either the granite being an unchanged remnant of a Plutonic mass from which the gneiss is derived, or the result of fusion of the gneiss. Evidence of unconformity between the beds of the limestone and the foliation of the

  1. ↑ Continued from page 314.
  1. ↑ Series of Peculiar Schists near Salida, Col., by Whitman Cross.In Proceedings of Col. Scientific Soc., Jan., 1893, pp. 1-10.
  2. ↑ A Geological Reconnaissance in the vicinity of Gouverneur, by C. H. Smyth, Jr.In Transactions N. Y. Academy of Sciences, vol. xii., April, 1893, pp. 97-108.

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