286 New York State Museum 



age. These soft, black shales are characterized by their 

 uniform, carbonaceous, fine-grained character. They 

 form a broad belt in the lower and middle Mohawk val- 

 ley. Toward the west these beds pass into the middle 

 and lower Trenton limestone; in the east they are over- 

 lain by the Schenectady beds. They pass up into the 

 Champlain valley and are found at Ticonderoga and espe- 

 cially on the Vermont side. Five graptolite zones (11 to 

 15) are represented in these shales, namely those of 

 Mesograptus mohawkensis, Diplograptus ample xicaulxs, 

 Glossograptus quadrimucronatus comutus, Lasiograptus 

 eucharis, Climacograptus spinifer. The fauna of the 

 Canajoharie is a very characteristic one, consisting be- 

 sides graptolites, of small individuals of brachiopods, 

 mollusks, trilobites and ostracods, suggesting unfavor- 

 able conditions of life as do also the black, carbonace- 

 ous, py rite-bearing shales. 



The Snake Hill beds (Ruedemann '12) contempora- 

 neous with the Canajoharie are shales, grits and sand- 

 stones deposited above the Normanskill shales in the east- 

 ern Levis trough and, as with the other shales, formerly 

 classed as part of the old "Hudson River" group. They 

 received their name from the very fossiliferous expos- 

 ures at Snake Hill on the east side of Saratoga lake. 

 Large and distinctive faunas have also been found around 

 Albany, Green Island, Mechanicville, Cohoes etc. These 

 beds are lithologically similar to the Normanskill shales 

 but are without the strong development of grits and 

 white- weathering chert beds; argillaceous shales prevail. 

 The black, carbonaceous, graptolite-bearing bands occur 

 more frequently than in the Normanskill formation, but 

 the graptolite fauna, comparatively, is much impover- 

 ished. On the other hand small gastropods, brachiopods 



