64 C. II Smyth, -Jr. — Gabhros in the Adirondack Region. 



stated, for the dense forest covering the region, the scarcity 

 of trails and the decided similarity in weathered surfaces of 

 the different rocks combine to make it a matter of great diffi- 

 culty to collect reliable data in regard to their areal relations. 



The identification of rocks of the gabbro family in this 

 locality is of interest in being one more piece of evidence indi- 

 cating a much wider range for this group in the Adirondack 

 region than was formerly supposed to be the case. In the 

 early days of the New York survey the anorthosite was de- 

 scribed by Emmons,* under the name hypersthene rock, as 

 limited to Essex County. Colvinf speaks of finding it in 

 another county, but does not state which one. Beecher and 

 Hall;}; in describing the faults of the Mohawk valley speak of 

 the labradorite at Little Ealls, but give no description of the 

 rock. Tan Hise§ has stated recently that in company with 

 Prof. G. H. Williams, he noted the gabbro in contact with 

 limestone at Bonaparte Lake, Lewis County. !N"ason| mentions 

 the occurrence of " frequent outcrops of the typical labrado- 

 rite rocks" along the line of the Cartilage and Adirondack 

 railroad, in Lewis and St. Lawrence Counties. Finally, the 

 work of Professor Kemp, already referred to, has shown a 

 great expanse of the gabbros in the vicinity of Lake Cham- 

 plain. In all of these recent papers, with the exception of 

 the last, the reference to the gabbro is merely incidental, and 

 no descriptions of the rock are given. They serve, however, 

 to indicate that this group of rocks is by no means limited to 

 Essex County, but, on the contrary, extends over a large por- 

 tion of the Adirondack region. Of the various localities men- 

 tioned, Little Falls is the nearest to Wilmnrt Lake, and is 

 therefore of most interest in this connection. The rock so 

 well exposed in the gorge of the Mohawk river at this place is 

 very coarse grained, usually distinctly gneissoid, and of a 

 greenish-gray color. It is composed chiefly of plagioclase, 

 with some pyroxene, hornblende, mica, and quartz. Its most 

 conspicuous feature is a highly developed cataclastic structure, 

 showing great " augen " of feldspar lying in a mosaic of finely 

 crushed fragments. In composition and structure the rock is 

 precisely like the Canadian anorthosites, in fact the figures of 

 cataclastic structure given by Adams^T might have been drawn 

 from sections of the Little Falls rock, so close is the resem- 

 blance. But more important is the fact that it is practically 



* Geology of New York, 2d District, p. 32. 

 f Adirondack Survey, Second Eeport, p. 151. 

 \ Fifth Annual Report State Geologist, p. 8 . 

 $ Bull. 86. U. S. G. S., p. 399. 



|| Iron-Bearing Rocks of the Adirondacks, Am. Geol., xii, p. 28. 

 T[ F. D. Adams, Ueber das Norian oder Ober-Laurentian von Canada, Neues 

 Jahrhuch fur Mineralogie, etc., B.B. vim, s. 419. 



