189 6. J Petrography. 477 



newly formed albite, zoisite and white mica. The final stage of the 

 alteration is a zoisite-amphibole rock. The green schists are composed 

 of ellipsoids of zoisite, feldspar and epidote imbedded in a schistose 

 green ampbibole clinochlor aggregate. Some of the schists are rich in 

 garnets, and others are practically chlorite-schists. All are supposed 

 to be derived from the gabbro. 



In addition to the gabbros there are also in the region several ex. 

 posures of serpentine whose contact with the green schists with which 

 they are associated are always sharp. The original form of the rock is 

 unknown, but it is supposed to have been a peridotite. Its most inter- 

 esting feature is the possession of light yellow and brown crystals of 

 some member of the.humite family. 



On the west side of the Matterhorn the author also found normal 

 and olivine gabbros, both more or less altered. The former is cut by 

 little veins of aplite. The peak of the Matterhorn is scarred by numer- 

 ous fulgurites. Its rocks are fine grained green schists, some of which 

 are like those described above, while others are dense and homogeneous 

 in appearance. They consist of amphibole, clinochlor, zoisite, altered 

 plagioclase, talc and alkali-mica. These rocks are defined as zoisite- 



The Rocks of Glacier Bay, Alaska.— Cushing 4 gives a few 

 additional notes on the petrography of the boulders and rocks of 

 Glacier Bay, Alaska. The principal rocks of the region are diorites, 

 altered argillites and limestones that are cut by dykes of igneous rocks. 

 In addition to the diorites and quartz-diorites reported by Williams 5 

 from this vicinity, there are also in the region mica and actinolite- 

 schists. The dyke rocks are mainly diabases. The author gives some 

 additional information concerning the diorites and briefly describes the 

 schists. The actiuolite schists are aggregates of finely fibrous aetinolite 

 needles, in whose interpaces is a granular mixture of quartz and epi- 

 dote and an occasional grain of plagioclase. The mica schists present 

 no unusual features except that some of them are staurolitic. 



Petrographical Notes. — As long ago as 1836 Thomson reported 

 the occurrence of light yellowish-green rounded masses which he called 

 huronite, imbedded porphyritically in a boulder of diabase from Drum- 

 mond Island. Other occurrences of the same substance have been 

 found by the Canadian geologist in diabase dykes cutting the rocks of 

 the Lake Huron region. These have been investigated by Barlow* 



4 Trans. N. Y. Acad. Sci., Vol. XV, p. 24. 



8 Cf. American Naturalist, 1892, p. 698. 



