GEoLOGY OF THE NORTH CREEK QUADRANGLE 43 



1 From western base of Heath mountain, North Creek sheet, Warren 

 county. Analyst Morley. 



2 From summit of Mt Marcy, Essex county. Analyst Leeds. N. Y. State 

 Mus, 30th Annual Rep't, p. 102. 



3 From shore of Upper Chateaugay lake, Clinton county. Analyst Eakle. 

 x\mer. Geol. July 1893, P- 35- 



4 From Palmer Hill, Black Brook township, Clinton county. Analyst 

 Kemp. U. S. Geol. Surv. Bui. 107, p. 26. 



5 From Bellmont township, Franklin county, dike 13. Analyst Morley. 

 N. Y. State Geol. i8th Annual Rep't, p. 120. 



6 From shore of Upper Chateaugay lake, Clinton county. Analyst Eakle. 

 Op. cit., p. 35. 



The North Creek sheet diabase (no. i) is lower in Al.Og and 

 CaO, and higher in TiOg than any of the others. It is also some- 

 what more acid than usual for the diabases, due to the more acid 

 character of the plagioclase feldspar. 



Lack of variation of the diabase 



Because of its remarkable homogeneity in composition, the dia- 

 base presents a marked contrast to the neighboring gabbro. The 

 diabase never contains inclusions and, with a single very local ex- 

 ception below described, never shows any evidence of magmatic 

 assimilation even in the largest masses. This difference is quite 

 certainly due to the difference in the mode and condition of intru- 

 sion, the diabase having clearly been forced through comparatively 

 narrow fissures in the country rock and near the earth's surface as 

 the texture shows. In such intrusions magmatic stoping would be 

 reduced to a minimum or absent. 



Contact phenomena 



A small dike, 53/2 inches wide, which cuts the Grenville limestone 

 at the asbestos mine three-quarters of a mile southeast of Thur- 

 man, shows contact phenomena which deserve special mention. Fol- 

 lowing is a description based upon thin sections and hand specimens 

 (see plate 7). 



Zone I This is typical, unaltered, medium grained, greenish gray, 

 serpentine marble. 



Zone 2 This zone, about one-third of an inch wide, lies along the 

 contact with the diabase. It consists of a fine grained, dark green, 

 well-baked serpentine marble. 



Zone 3 One-sixth of an inch wide. Nearly black (greenish 

 gray in thin section), glassy looking dike rock which shows an irreg- 

 ular but sharp boundary against the marble. It appears to consist 



