GEOLOGY OF FRANKLIN COUNTY 109 



A small mass of an ordinary quartzose augite syenite, quite like 

 much of the rock around Loon lake, occurs near Lower Ohateau- 

 •gay lake in Belmont township. Quite likely similar small in- 

 trusions will be found elsewhere when the county is more care- 

 fully surveyed. 



The precise age of these syenite intrusions is not yet known. 

 -At Loon lake they cut the Grenville rocks/ and elsewhere the 

 doubtful gneisses, and are hence younger than either. The 

 gabbros to be next described have been reported by Smyth as 

 -cutting the Diana augite syenite in Lewis county. 2 The syenite 

 is therefore older than these gabbros. The unsettled point 

 •concerns their relation to the anorthosites. As to this, evidence is 

 so far lacking in Franklin county, and so far as the writer is 

 aware in the rest of the Adirondacks as well. The areal distribu- 

 tion of the two in Essex and Franklin counties is however so 

 involved, that localities will certainly be found in which this im- 

 portant evidence will be forthcoming. ,The main difficulty arises 

 from the puzzling peripheral phases which both rocks exhibit. 3 



Gabbros. These are basic and dark colored, often black, rocks 

 of quite variable composition and structure. Though their areal 

 extent is not great, they are of common occurrence throughout 

 the Adirondacks, and have been more frequently and exhaustively 

 described than any of the other igneous rocks of the region. 4 



As seen in Franklin county these gabbros occur either as dikes 

 or as small intrusive bosses. They are wholly distinct from the 

 gabbro-gneisses which occur as border facies of the anorthosites. 

 The dikes are the more common, but the bosses are by no means 

 infrequent, and beyond doubt many more remain to be discovered. 



The dikes are almost without exception very fine grained, black 



iCushing, H. P. Bui. geol. soc. Amer. 10:185. 



2 Smyth, C. H. jr. Bui. geol. soc. Amer. 6:283, 



3 Kemp, J. F. Bui. N. Y. state museum no. 21. 1898. 5:283. 



4 Kemp. J. F. Amer. jour, sci, Aug. 1892. 44:109-14. 

 Bui. geol. soe, Amer. 5:213-24. 



Smyth, C. H. jr, Amer. jour. sci. 1894, 48:54-65. 



Bui. geol. soc. Amer. 6:268-83. 



Amer. jour, sci., 4th ser. 1:273-81. 



