LOWER SILURIC SHALES OF THE MOHAWK VALLEY 65 



even interfolded so that they form narrow alternating strips. We 

 therefore infer that the Snake Hill beds lie closer to the Norman- 

 skill shales than the Canajoharie shales and are older than the 

 latter. 



3 At Hudson Falls and near Saratoga the Canajoharie shales 

 rest directly on the Glens Falls limestone. The latter is according 

 to Ulrich's determination, of very early (basal) Trenton age. 



Since now the Canajoharie beds rest directly on the Glens Falls 

 limestone and the Snake Hill beds are older than the Canajoharie 

 beds, they must be absent in the western part of the Saratoga basin 

 as well as in the Mohawk valley. Because of the fact that the 

 Snake Hill beds are interfolded with the Canajoharie beds at the 

 lower Mohawk and the western edge of the Hudson valley, we 

 have considered them at first as deposited about the eastern edge 

 of the Mohawk basin and as intercalated there between the Glens 

 Falls limestone and the Canajoharie shale. Subsequent work, how- 

 ever, especially the summer's work of 191 1 on the Schuylerville 

 sheet, has shown that these shales reappear in a distinct belt on the 

 east side of the Normanskill belt. They are therefore deposits of the 

 same basin as the Normanskill shale. This inference is in accord 

 with the observation that nowhere Snake Hill beds have been 

 observed between the Glens Falls limestone and the Canajoharie 

 beds, and it also accords with the faunal evidence that the Snake Hill 

 sea had connections toward the north and east and thence received an 

 important portion of its fauna. This latter evidence consists 

 in the presence in the shales of Edrioaster, Carabo- 

 crinus, Eoharpes ottawensis and O r t h i s 

 (Plaesiomys) retrorsa, all of which point to the St 

 Lawrence and Ottawa Trenton rather than to the central New York 

 Trenton. It is also noteworthy in this connection that P r o e t u s 

 undulostriatus, of which we have obtained a well preserved 

 carapace in the Snake Hill beds, is also known from the black pebbles 

 (Black river?) of the Rysedorph Hill conglomerate and that the 

 latter in its faunal connections also points east. Likewise C 1 i m a - 

 cograptus caudatus is in America known only from the 

 Snake Hill beds and the Magog shales in Canada and is an Atlantic 

 form. Cryptograptus tricornis and Climaco- 

 graptus scharenbergi have been directly taken from 

 the Normanskill sea. 



