Analytical Abstracts of Current 

 Literature. 



Summary of Current Pre -Cambrian North American 

 Literature.^ 



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 inter- 

 bedded 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 con- 

 sisting 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 



* 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. 



532 



