LOWER SILURIC SHALES OF THE MOHAWK VALLEY I3 



various sections clearly show that along the western border of the 

 Appalachians, dark graptolite shales continued to form in Upper 

 Ordovicic time, while westward from this the Trenton limestone 

 represents the calcareous phase of the Utica-Trenton series (see 

 map, figure 8) . 



In a diagram that accompanies Professor Grabau's paper (op. 

 cit. figure 9), the Utica is represented as wholly replaced by Tren- 

 ton limestone in the latitude of Rochester and farther west. 



In the description of the Remsen quadrangle Miller (title 65) has 

 shown the absence of the Dolgeville beds in the area adjoining the 

 Little Falls quadrangle to the west. He found the Utica to be only 

 300 feet thick indicating a notable thinning to the northwest from 

 the type section. Two hundred feet of Lorraine beds were observed 

 which were found to be destitute of fossils and are not separated 

 by an exact boundary line from the Utica. There is little doubt 

 that these beds are the Frankfort shale. This decrease is in a later 

 bulletin (title 66) by the same author shown to be steady toward the 

 north. It would also become probable from the same paper that 

 the Frankfort shale with a thickness of about 200 feet continues 

 to the northwest and intervenes there between the Utica shale and 

 Lorraine sandstones and shales with the characteristic Lorraine 

 fauna (page 33). 



To the south of New York, in New Jersey, Pennsylvania and 

 West Virginia, the shales which formerly were termed " Utica and 

 Hudson River slates" are now known as Martinsburg shale. The 

 Martinsburg shale of the Mercersburg-Chambersburg quadrangle 

 in Pennsylvania has been described by Stose, and fossil lists given 

 by Ulrich (title 61, page 10). The lowest shale fauna is con- 

 sidered as indicating an age corresponding to that of the lower to 

 middle Trenton of New York, and the highest as comprising species 

 characterizing the Eden shale. 



Bassler, in his work on the Cement Resources of Virginia 

 (title 62), the Federal Survey's part of which was done under the 

 official direction of Doctor Ulrich, divides the Martinsburg shale 

 in three divisions, namely, upper Trenton shale, Utica shale and 

 Eden shale, representing the shaly Ordovicic deposits of the 

 Appalachian trough. The Martinsburg is continuous from Vir- 

 ginia through Pennsylvania and New Jersey with the shale belt 

 of New York, and this division of the shales has a direct bearing on 

 that of the shale in the New York part of the Appalachian trough, 

 represented by the shales in the Hudson valley. 



