GEOLOGY OF SARATOGA SPRINGS AND VICINITY 69 



A comparison of the two series of divisions, that for the slate 

 belt of Washington county and Vermont and that for Rensselaer 

 county, furnished by Dale, shows that the olive grit in the first 

 is overlain by a great mass of colored slate, the '' Cambric roofing 

 slates," and in the latter rests on a still greater mass of colored 

 shales ; further that the Cambric roofing slates and the Black patch 

 grit are absent in the latter series, where a granular quartzite 

 10 to 40 feet thick and a second mass of colored shales 25 ? to 

 100+ feet thick intervene between the olive grit and the black 

 shale and thin-bedded limestone. In Washington county this is 

 followed by another quartz mass, the ferruginous quartzite, and 

 in Rensselaer county by greenish shale. 



In accordance with the present practice to name the units after 

 their type localities instead of their lithologic and faunistic char- 

 acteristics and to avoid confusion between the different horizons 

 of colored shales and quartzites, we propose here the following 

 names for these units : 



1 Bomoseen grit (olive grit). Olive green grit, nearly a pale 

 brick-red. Associated with it in places a bed of quartzite 12 to 

 55 feet thick. 50 to 200 feet. The type locality of this unit is, 

 according to Dale, on the west side of Lake Bomoseen, Vt., " one- 

 quarter of a mile west of the road running north from Hydeville, 

 on the north side of road to Fairhaven." It is finely exposed about 

 Greenwich, N. Y., especially in ridges northwest of that town, 

 and south on Louse hill, but disappears in Rensselaer county where 

 it still outcrops east and southeast of Troy. 



2 Mettazi'ee slate (Cambric roofing slate Dale). See definition, 

 page 67. These slates extend typically from Pawlet, Vt., and 

 Granville, X. Y., to Fairhaven, \t. The town of Granville, which 

 is the center of the industry, would furnish a good name if it were 

 not preoccupied. We have therefore taken the name of the Met- 

 tawee river which drains the region. 



3 Eddy Hill grit (Black patch grit). This formation, which is 

 defined on page 67, is termed from Eddy Hill, near Fairhaven, 

 Vt., where it is seen to rest on the Mettawee slate, and carries 

 fragments of the Olenellus fauna. Its extension southward is 

 not safely established on account of its great similarity to the 

 " Hudson " grit. 



4 Schodack shales and limestones (Cambric black shale). De- 

 fined on page 67. This formation of black shales and lime- 

 stones always occurs near the top of the Georgian ; it is well 



