LOWER SILURIAN SYSTEM OF EASTERN MONTGOMERY CO. 427 



hibiting a brownish or dark chocolate color by alteration or long 

 exposure to the weather. . . It is associated with thin beds of 

 the same kind of colored impure limestone which are usually found 

 in the lower part of the mass. . . The slate often presents thin 

 veins of white lamellar carbonate of lime. . . [It has] a thickness 

 whose maximum is about 250 feet."^ 



Of this mass Emmons says, ** It would do no violence to geo- 

 logical classification to incorporate it with the Trenton limestone 

 below or with the Lorraine shales above"; however, "this mass 

 is well developed in the valley of the Mohawk. "^ 



In Mr Barton's paper it is stated that '' Its Utica characters 

 are quite unmistakable throughout the Mohawk valley. They are 

 very dark, even bedded slates and shales, with alternating slabby 

 beds at most localities."^ 



The following estimates of the thickness of the Utica formation 

 are given because of their bearing on the estimates which will 

 be given in a later part of the present paper, though some of them 

 do not apply to this region. Vanuxem's estimate of 250 feet in 

 Montgomery county has already been quoted. In a summary of 

 the thickness of the formations of the " Champlain division " 

 Emmons estimates the Utica shale at 100 feet,^ and in another place 

 he says *' The slate [Utica] in the gorges of Lorraine and Rodman 

 is about 75 feet thick; it is at least less than 100 feet."^ Dana 

 gives the thickness of the Utica formation as 250 feet in Mont- 

 gomery county. 6 Other estimates are those of Mr C. D. Walcott 

 and Prof. C. S. Prosser, derived mainly from well records. 

 Walcott gives the thickness of Utica passed through in the Camp- 

 bell well near Utica as 710 feet,"^ and in a diagram in the latter paper 

 indicates that the formation thickens eastward (p. 350, diag.). In his 

 section along the south branch of Sandy creek in Jefiferson county 

 Walcott gave 180 feet of Utica shale with 100 feet of transitional 

 beds composed of " alternating bands of shale and gray, fine 

 grained, calcareous sandstone, the shale predominating " (p. 348 and 

 diag. p. 350). Prosser gave the thickness of the Utica shale in the 



^Geology of New York, pt 3, p. 56. 



"Agriculture of New York, 1:123, 124. 



813tli annual report N. Y. state geologist, 1893, p. 429. 



^Agriculture of New York, 1:127. 



"Geology of New York, pt 2, p. 118. 



^Manual of geology, ed. 4, p. 494. 



^Am. ass'n adv. sci. proc. 35:212; also Geol. soc. Amer. bul. 1890, 1:347. 



