90 NEW YORK STATE MUSEUM 



pounds to the square inch. The chemical composition, as determined 

 by L. K. Russell is as follows : 



Si02 66.78 



AI2O3 13.01 



FeaOs 6.50 



MgO .92 



CaO 1. 31 



NasO, K2O 10.89 



H.0 51 



Total 99.92 



The quarry is owned by the St Regis Red Veined Granite Co., 

 and the output thus far has been mainly monumental stock. 



GRANITIC ROCKS IN THE EASTERN ADIRONDACKS 

 The eastern Adirondack region, or so much of the highland as 

 is included in the Lake Champlain drainage area convenient to 

 rail and water transportation, is made up largely of igneous rocks 

 belonging to the class of anorthosite, gabbro, syenite and granite. 

 Their intrusion took place in Precambric time before the final 

 stages of uplift and metamorphism that profoundly modified the 

 region during that period had been accomplished. Laminated gneis- 

 soid characters are very common; in fact there are comparatively 

 few localities where the igneous rocks show unchanged, massive 

 structure. The existence of unreduced or slightly modified residuals 

 affords a basis for quarry operations in connection with building 

 and monumental stone of the best quality, while there is an un- 

 limited supply of material suited to many purposes for which abso- 

 lute uniformity of texture or an attractive appearance is not es- 

 sential. 



Rocks of the anorthosite class are most widespread in this section 

 of the Adirondacks. They have a very simple mineral composition, 

 consisting almost wholly of basic plagioclase feldspar, usually labra- 

 dorite and in their unaltered phase are characterized by very dark 

 colors. The anorthosites spread over most of Essex county as a 

 single, practically unbroken, area that embraces all the more prom- 

 inent Adirondack peaks within its borders. They extend in force 

 westward into Franklin county, but have little representation in 

 Clinton county, the southern border of which is nearly coincident 

 with the northern limits of the main area. An outlying intrusion 

 of small compass occurs, however, in Beekmantown and Altona 

 townships of Clinton county about 30 miles north of the county 

 line. 



