170 Th( American Geologist. March, i»96 
Silurian : those of the center are much younger. In Iowa the 
general clip of the strata is towards the southwest. The de- 
gree and remarkable uniformity of the inclination has recently 
been determined by Norton*-* for the northeastern half of the 
state. The results are especially reliable for the reason thai 
the inquiry was undertaken for the purpose of determining 
the artesian water horizons; and the chief water-bearing 
stratum, the St. Peter sandstone, is easily traceable oyer the 
greater portion of the area on account of the numerous deep 
wells put down. In northeastern Missouri the dip is nearly 
west; and from the Ozark uplift northwestward. The place 
in which it would be expected that the Paleozoic rocks would 
show a maximum thickness, that is, the middle part of the 
basin, is in the neighborhood of the Missouri river between 
Kansas City and the Iowa boundary. 
The variation in estimates of the thickness of the stratified 
rocks below the base of the Trenton is as great as 1,100 feet. 
In Missouri, Swallow* and Broadheadf agreed in a measure- 
ment of about 1,400 feet. Other figures* which were based 
chiefly upon observations in the Iron Mountain region placed it 
at about 650 feet. It is quite probable that the latter number 
is considerably too small when the region in general is taken 
into consideration, and that a mean, or about 1,000 for the 
state, would more nearly harmonize with the actual tacts. 
Worthen§ allowed less than 300 feet for the same succession. 
but this manifestly only referred to the outcrop as shown in 
Illinois. In northeastern Iowa, Hall || placed the exposed meas- 
urement at a little less than 800 feet; while White* ascribed 
a thickness of about 600. To these figures, for the sedimen- 
taries beneath the Trenton in this part of the basin, should be 
added about as much again, as was subsequently shown by 
deep borings. It is quite likely, then, that the lower part of 
the geological column is somewhat thicker on the northern 
rim of the basin than on the southern. 
**Iovva Geol. Sur., vol. in, pp. 167-210, 1895. 
^Missouri Geol. Sur., 1st. and 2nd. Ann. Repts., p. 60, 1855. 
|Amebican Geologist, vol. xiv, p. 381, 1894. 
^Missouri Geol. Sur., vol. iv, p. 30, 1894. 
§Geol. Sur. Illinois, vol. n, p. 40, 1866. 
'( reology of Iowa, vol. t, p. 42. 1858. 
* ( reology of Iowa, vol. i, p. 20. 1872. 
