LOWER SILURIC SHALES OF THE MOHAWK VALLEY 37 



glomerate, is not yet well defined in regard to the Pulaski formation, 

 the question being to which of the two the shale with Trinucleus 

 northwest of Utica is to be referred. Doctor Ulrich writes that he 

 is inclined to place it with the Frankfort and to confine the Pulaski 

 to the overlying even more fossiliferous arenaceous limestone and 

 shale shown at Pulaski and in the upper part of the Lorraine gorge. 

 The problem of the correlation of the Frankfort formation, thus 

 restricted and defined, with the strata of Ohio has been discussed 

 very fully by Doctor Ulrich and the author. Doctor Ulrich recog- 

 nizes in the Frankfort s. str. the two middle divisions of the Eden 

 shale at Cincinnati, but he is convinced that it also includes the 

 upper Eden. The Eden, as used by Doctor Ulrich for a long time, 

 is confined to beds beginning at the top of the true Utica and 

 extending upward to the base of the Maysville. But as originally 

 defined the Eden included all the shales to the top of the underlying 

 Point Pleasant Trenton limestone in the Ohio valley; hence it in- 

 cluded also the thinning western representative of the true Utica. 

 For this reason Doctor Ulrich has proposed to use the term Eden 

 for a group comprising the Utica and Frankfort (title 69, plate 2'j'), 

 The Eden in Ohio is followed by the Maysville, which in New York 

 is represented by the Pulaski formation and Oswego sandstone. 

 The Lorraine, we infer from the above-cited chart, is retained as a 

 local or New York term only to comprise the Frankfort and Pulaski 

 formations. 



SCHENECTADY FORMATION 



As the black shale belt that follows the Mohawk river from 

 Utica to near its mouth has always been considered as being of 

 Utica age, but has been found to change in age from Utica to lower 

 Trenton in descending the river, thus the parallel and coextensive 

 belt of overlying, more argillaceous, olive gray shales has been 

 quite naturally identified with the Frankfort shale by all authors, 

 the present included, since these beds apparently form a continuous 

 belt, just as the underlying black shale does. When we discovered 

 in the great thickness of " Frankfort " beds in Schenectady and 

 ^Schoharie counties the eurypterid fauna associated with a con- 

 "^siderable number (see page 42) of graptolites, brachiopods, mol- 

 lusks and trilobites, different from those of the Frankfort shale, 

 we distinguished there several thousand feet of sandstones and 

 shales as the " Schenectady facies " of the Frankfort formation. 

 Closer investigation of the faunas, with the assistance of Doctor 



