GEOLOGY OF THE LAKE PLACID QUADRANGLE 



6i 



cut all the other types of Adirondack rocks as narrow bands of 

 slight area! extent. They are wholly nonmetamorphosed. 



The fresh rock is dark bluish gray and generally fine grained, 

 though a few of the larger dikes are medium grained toward the 

 middle. Many of the dikes are distinctly finer grained toward 

 their margins. A glassy groundmass occurs in a few cases. Many 

 of the rocks contain small phenocrysts of augite or olivine, or both, 

 and a few contain phenocrysts of plagioclase feldspar. A good 

 diabasic texture is often clearly discernible with the naked eye in 

 the relatively coarser grained rocks, and with the microscope in the 

 finer grained ones, though some O'f the dikes apparently fail alto- 

 gether to exhibit this texture. 



In width most of the dikes range from less than an inch to 25 

 or 30 feet, and in length up to at least one-half of a mile. Most of 

 the dikes show a general northeast-southwest strike, this being 

 parallel to certain prominent structure (fracture) lines of the 

 region. Some of the dikes strike nearly east-west, but not one was 



Table 6 Thin sections of. diabase 



d 

 c 



D 







E 





 nJ 



'5i 

 3 

 < 



c 









 S 



0) 



u 







o'c 



|l 



C 

 bo 

 d 



>. 



a. 



0, 



•0 







OJ 



a 



< 



61 



7 g 3 



17 J 6 

 10 m I 



Sf I 

 2 k 14 



I k 2 



68 

 60 

 60 

 58 

 6S 

 30 



20 



S 



21 



IS 



40 



I 

 5 



4 

 3 



7 



7 

 4 

 5 

 4 

 3i 

 6 





20 



I 







62 







63 



30 





64 



6S 

 66 



I 

 4 



3 

 16 

 20 



7 



little 



6 







little 



















No. 61, dike no. 33, High fall of West Branch Ausable river; no. 62, 

 dike no. 48, i>^ miles southeast of Fremont hill; no. 63, dike no. 24, 

 quarry at southern base of Hamlin mountain; no. 64, dike no. 5> one-half 

 of a mile south-southwest of Owen pond; no. 65, dike no. 14, i 'mile 

 north-northwest of Keene; no. 66, dike no. 9, one-half of a mile south 

 of Keene in the gorge. 



observed to strike northwest-southeast. Many of the intrusions 

 quite certainly took place along zones of faulting of excessive 

 jointing, but in some such cases, at least, renewed earth move- 

 ments occurred after the intrusion of dike material because the 

 dike rocks themselves, in such cases, are either brecciated or exces- 

 sively jointed. 

 As seen in table 6, the chief minerals are labradorite and augite. 



