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 Darton’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 
ravent 75 -teet thick; itis 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 
aud Proi.. C: “S: Prosser, derived mainly trom 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 Jefferson 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 
1Geology of New York, pt 3, p. 56. 
2Agriculture of New York, 1:128, 124. 
813th annual report N. Y. state geologist, 1898, p. 429. 
4Agriculture of New York, 1:127. 
5Geology of New York, pt 2, p. 118. 
®Manual of geology, ed. 4, p. 494. 
7Am. ass’n adv. sci: proc. 35:212; also Geol. soc. Amer. bul. 1890, 1:347. 
