Kemp — Geology of Essex County. 



587 



The ridge of W ilmington mountain in the northerly portion has been 

 traversed at No. 43b. The rock is gneissoid with the usual minerals of the 

 gabbros. In the pass at No. 44, the gneissoid structure also holds, and in 

 thin section the rock shows labradorite, hypersthene, garnet and brown horn- 

 blende. At No. 4fi it is chiefly labradorite. 



The rock of Whiteface mountain is quite different from the usual types 

 elsewhere in the mountains. It is a markedly white rock through which are 

 distributed dark bunches of ferro-inagnesian silicates up to half an inch or 

 more across. It looks like a light granite. It is not strongly gneissoid, 

 although faint lamination is distinctly visible. Under the microscope it 

 exhibits plagioclase, brown hornblende, pale lavender augite, magnetite, 

 presumably titaniferous, and titanite. Pegmatite veins, strongly quartzose 

 run through it at the summit. The rock on the way up from Wilmington, at 

 No. 47a, is strongly laminated, with a nearly noi'th and south strike. On the 

 trail down to French's, at No. 49, k a very gneissoid type, with a true strike 

 of N. 25° E. 



The rock under ihe microscope is chiefly untwinned but very coarsely 

 microperthitic feldspar with an extinction on the cleavage, up to seven 

 degrees, so that it appears to be orthoclase. The inclusions are spindle- 

 shaped, but curve and are irregular. Their general alignment ranges up to 

 twenty-five degrees with the line of extinction of the enclosing feldspar. The 

 other minerals are diallage and a few shreds of quartz. The rock is very 

 puzzling, exhibiting as it does the characters of both the gneisses and gabbros. 

 Future and more thorough exploration may lead to the determination of some 

 of this great ridge on its northwesterly side as belonging to the series of 

 gneisses. It needs more exploration, but as it is a heavily wooded district and 

 remote from settlements, it is less accessible than many other districts. I 

 have provisionally colored it as belonging to Series III, as such is my 

 opinion from observations thus far made. The same rock that forms the 

 peak of Whiteface mountain extends well down to the shores of lake Placid, 

 and further along the ridge to the northeast in the pass, the rocks, as already 

 stated, have the mineralogy of the gabbros. 



After leaving Station 49 no more actual outcrops were crossed by the 

 trail which passes down through thick woods. All the boulders that were 

 met, and some could not have been far from their parent ledges were gneissoid 

 rocks of the mineralogy of the gabbros. But soon after leaving No. 49, the 

 trail passed into St. Armand. 



Series IV entirely fails in Wilmington. 



