Apparent Anomalies of the Postville Well. — Calvin. 197 
series, t lie division commonly known in western geology as 
the Trenton limestone. All previous measurements of the 
thickness of the sediments between the base of the Galena and 
the upper surface of the Saint Peter fall far short of the 345 
feet disclosed by the Postville section. Furthermore, these 
older measurements indicate a very remarkable range of vari- 
ation in the thickness of this part of the geological column. 
For example, Hall's section at Clayton City* shows only about 
20 feet of Trenton, while that at Guttenberg,f only eight or 
ten miles southeast of Clayton, shows 116 feet between the 
Galena and the Saint Peter. Strong makes the Trenton in the 
lead region of Wisconsin fifty feet thick,* while White§ re- 
ports the thickness of the Trenton along the Mississippi as 
eighty feet, and in Winneshiek county as upwards of 200 feet. 
That the thickness of the Trenton in Winneshiek county is 
more than 200 feet is quite certain: for in the great vertical 
cliff at Bluffton there is an exposure of more than 150 feet, 
made up wholly of limestone beds belonging to No. 4 of the 
Postville section. The Bluffton clifi' exposes neither the bot- 
tom nor the top of this member of the Trenton, and yet be- 
tween Bhrffton and a point three miles below Decorah tin- 
lower portion of number 4 and the whole of numbers 1, 2 and 
3 are exposed and shown to be fully developed. There are at 
least eighty or ninety feet of Trenton below the beds exposed 
at Bluffton, and that the beds corresponding to numbers 5 to 
8 inclusive are present in considerable force, is attested by 
many observations, though the exact thickness of the beds 
has not been ascertained. In the report on the Geology of 
Allamakee county || the writer made the total thickness of tie 
Trenton about 300 feet, the thickness of No. 4 of the Pn-t 
v i 1 1 e section having been measured in the eastern part of the 
county where it is at least 50 feet thinner than in Winneshiek 
and southwestern Allamakee. According to Norton*: the well 
records in (-astern and northeastern Iowa demonstrate that 
*Hall's Geology of Iowa, vol. i. pari 1. p. 56, 1858. 
tlbid., p. 58. ' 
JGeology of Wisconsin, vol. n. p. 680, 1877. 
gGeology of Iowa, vol. i, |>. 175, 1870. 
Iowa Geol. Surv., vol. iv. General Description of the Trenton, pp. 
74-77, 1895. 
• Iowa Geol. Surv., vol. in, p. 180. 1895. 
