52 Washington — Study of the Glaucophane Schists. 



Rosenbusch calculated the rock composition from the specific 

 gravities of the rock and of the two minerals, and their known 

 chemical composition. He gives two limiting results, but, as 

 they differ but little, that corresponding to the mineral mix- 

 ture Ab 76 Cr 25 is here given. As Rosenbusch remarks, this com- 

 position is quite anomalous, whether for eruptive or meta- 

 morphic rocks, and it is to be desired that an analysis of the 

 rock itself were available. 



Oregon. 



Glaucophane schists, both acid and basic, occur along the 

 coast in Oregon, and have been partially described by Diller,* 

 who suggests that, as at Angel Island, they are the products of 

 contact metamorphism. He very kindly sent me a number of 

 typical specimens, three of which I have analyzed. 



That from a ledge about one mile N.E. of Winston's bridge, 

 near Roseburg, is a schistose, gray (scarcely blue) fine-grained 

 rock, with many glistening flakes of white mica sprinkled 

 through it. One specimen shows some small brown garnets. 

 The other (analyzed) is wanting in them, and is composed of a 

 felt of stout, rather short glaucophane crystals, with grains of 

 epidote, some chlorite, a few irregular quartz grains, and 

 phenocrysts of colorless mica. 



Chemically (I) it is the most basic of all these rocks which 

 have been analyzed with the exception of the one partially 

 analyzed by Rosenbusch. It is also very high in iron, low in 

 CaO, and, for these rocks, high in K,0, which indicates that 

 the mica is a muscovite and not a paragonite, as in the Syra 

 rocks. 



Glaucophane schists also occur southwest of Roseburg, in 

 the neighborhood of Coos Bay. Those from Tupper Rock 

 have been briefly described by Diller, and three specimens sent 

 me indicate that they vary considerably in character. Two are 

 composed essentially of glaucophane embedded in granular 

 quartz, with some white mica, and a little epidote. The 

 chemical composition of these must be closely similar to that 

 from Four Mile Creek, described later. The other (III) is 

 much more basic, composed of glaucophane with less granular 

 epidote, or zoisite, in which lie many small garnets, around 

 which are zones of white mica. This corresponds more nearly 

 in chemical composition to the Mount Diablo occurrence.' 



The schist from Four Mile Creek, Coos County, is a rather 

 coarser grained, schistose rock, of a general light gray color, 

 showing considerable white mica and quartz. In general 



* Diller, 17th Ann. Rep. U. S. G. S., i, p. 454, 1896 ; Geol. Atlas of U. S. Rose- 

 burg Folio, 1898. 



