10:.' The American Geologist. August, i8«3 
In considering now the character of the physical break at 
the base of the ('<>al Measures in Iowa and Missouri, attention 
must be directed briefly to a few of the leading sections 
showing the line of contact between the two formations. 
Oih- of the most important exposures bearing upon the 
question under consideration has been fully described in con- 
nection with the cross-seed ion of the Lower Coal Measures of 
the central part of the state.* It was shown that in Marion 
county between Harvey and Bedrock, a distance of ten miles. 
not less than 75 feet of shales were represented between the 
two different horizons of the Coal Measures reposing against 
the St. Louis limestone. The great part of the vertical dis- 
tance just referred to appeared to be due to irregularities in 
the limerock, which were carved through erosion prior to the 
laying down of the Coal Measures. 
Near Fairfield, in Jefferson county, the Coal Measure clays 
with their seams of carbonaceous matter rest directly upon 
the uneven surface of the St. Louis marls which cap the lime- 
stone of the same age, and which contain fossils in abundance. 
At various places in Keokuk and Mahaska counties borings, 
as well as exposures, indicate that the irregularities in the sur- 
face of the St. Louis limestone are even greater than they are in 
Marion county, as already explained. The borings just referred 
to are quite numerous and special care has been taken for the 
reason that search was in progress for a "second" vein of coal 
— a scam supposed to be much lower than the one at present 
being worked. In one place where the St. Louis limestone 
was exposed at the surface, operations with a diamond drill 
had begun in hopes of reaching the "lower" coal bed. The 
reason given for carrying on the work in this manner is that 
a mile away the coal at present worked was many feet lower 
down than the limestone outcrop and therefore the coal bed 
must lie beneath. 
Relations similar to those above described have also been 
observed in connection with the St. Louis limestone and Lower 
Coal Measures at Ft. Dodge and elsewhere in "Webster county. 
Similar cases might be cited again and again, if it were nec- 
essary, in the present connection. 
*Bul. Geo!. Soc. America, vol. in, pp. 283-310. 1892. 
