Washington — Study of the Glaucophane Schists. 49 



by contact metamorphism of a dolerite, at Mansfield, Michi- 

 gan, described by Clements.* The adinole carries abundant 

 albite, and actinolite instead of glaucophane. This difference 

 may be connected with the higher A] a O, and Na 2 and lower 

 FeO in the adinole. 



Angel Island* Col. — The occurrence just described seems to 

 be analogous with that at Angel Island, in San Francisco Bay, 

 described by Ransome,f the similarity being also remarked on 

 by Smith (p. 57). At the latter locality radiolarian cherts 

 have been altered into quartz-glaucophane schists by the intru- 

 sion of fourchite and serpentine. They vary rather more in 

 character, as some are composed essentially of glaucophane and 

 albite,J while others are made up of glaucophane and quartz. 

 Brown mica and garnet also occur. Analysis II above, by 

 Ransome, shows the essentially general similar character of the 

 two,' though it was made evidently of an albitic schist. 



It is of interest to note that, just as carbonaceous matter is 

 preserved in the Santa Catalina schists, so in these from Angel 

 Island the radiolarian remains are not entirely obliterated by 

 the metamorphism. 



Mount Diablo. — Among the metamorphic rocks of this 

 locality glaucophane schists occur,§ but unfortunately detailed 

 petrographic descriptions seem to be wanting. One of them, 

 a bowlder from Pine Canyon, has been analyzed by Melville. || 

 It is briefly described as bluish with streaks of green, with well 

 marked schistose structure, and containing innumerable cinna- 

 mon garnets. It is composed presumably chiefly of glauco- 

 phane, epidote and garnet, with few accessories, and is probably 

 closely similar to some of the glaucophane schist of Tupper 

 Rock, Oregon, or a specimen from Tiburon Peninsula, sent 

 me by Prof. Lawson. The analysis is given on the next page. 



In a recent paper 1 ]" Turner throws some doubt on the inter- 

 pretation of these schists as the product of contact metamorph- 

 ism by basic intrusions, but discussion of this problem is 

 outside the scope of this article. 



Sulphur Bank. — Glaucophane schists from this locality, 

 which lies east of Clear Lake (north of the preceding locality), 

 have been described by Becker.** They vary much, as else- 

 where, some being quartz-mica-glaucophane schists, and others 



* Clements, this Journal, IV, vol. vii, p. 88, 1899. 

 f Ransome, Bull. Dept. Geol. Univ. Cal., vol. i. p. 211, 1894. 

 f Turner (17th Ann. Rep. U. S. G. S., i, p. 728, 1896) suggests that they may 

 be in reality dike rocks. 



§ Turner. Bull. Geol. Soc. Amer., vol. ii, p. 384, 1891. 

 fl Melville, Bull. Geol. Soc. Amer., vol. ii, p. 413, 1891. 

 •ff Turner, Jour. Geol., vol. vi, p. 490, 1898. 

 **G. F. Becker, Mon. XIII, U. S. G. S., p. 102, 1888. 



Am. Jour. Sci.— Fourth Series, Vol. XI, No. 1 —January, 1901. 



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