382 NEW YORK STATE MUSEUM 



feet thick, and perhaps more, the line between the Trenton and 

 Beekmantown being difficult to draw with precision in that well. 

 At Vernon, 17 miles west of Utica, 350 feet of the well section 

 are assigned to the Trenton, and at Rome, 11 miles northwest of 

 Utica, 375 feet. These thicknesses are not so great as those far- 

 ther to the north, but the sudden increase in thickness between 

 Ilion and Utica is quite analogous to that between Middleville 

 and Trenton falls, along the more northerly line. At Chitten- 

 ango, 35 miles west of Utica, the drill passed through 636 feet of 

 apparent Trenton, and rested in that rock, a thickness directly 

 comparable Avith that shown in Oswego and Jefferson counties. 



Utica formation. Tlhiis formation is, as a whole, surprisingly 

 homogeneous all about the Adirondacks, consisting of fissile, 

 black, somewhat calcareous, clay shales, which, like most car- 

 bonaceous shales, tend to split thinly and evenly and to have a 

 somewhat slaty character. They become usually more fissile 

 and less calcareous above, while below thin bands of shaly, 

 black limestone commence to appear and increase in abundance, 

 forming more or less of a transition to the Trenton beneath. 

 Definite passage beds 'of the sort, of considerable thickness, are 

 often found, but the evidence is not decisive as to whether they 

 are, or are not, everywhere present in force. More likely they 

 are not, and this seems specially probable on the west side of 

 the region, and also pi. the lower Mohawk valley; whereas in the 

 Champlain valley and the upper Mohawk region they have much 

 importance. These beds are also a mixture faunally. the rather 

 restricted fauna which characterizes the pure Utica occurring 

 with a consiiderable number of Trenton forms, so that the line of 

 demarcation between the two formations will vary greatly, 

 according as it is drawn at the first appearance of the Utica 

 fauna, on the one hand, or at the final disappearance of the Tren- 

 ton fauna on the other. The case is one where it seems certain 

 that the two contrasted faunas were living in the same basin at 

 the same time, each in situations where the conditions were 

 favorable, and each under different sorts of conditioniSi; and that 

 the one set of conditions increased in area occupied, and its 

 fauna spread, at the expense of the other. 



In the Ohamplain valley it is difficult to arrive at any precise 

 motion regarding the thickness of the formation. It is the 



