242 Keyes—Stratigraphy of the Kansas Coal Measures. 
the “ Lower” and “ Upper” Coal Measures do have a relation 
of one above the other and from a mining standpoint of an 
upper and a lower member, they do not hold positions indicat- 
ing that as a whole the one is geologically older than the other, 
or that the lower was deposited before the upper. On the 
other hand, the facts show clearly that the terms lower and 
upper are misnomers in the sense that they are usually used, 
carrying with them as they do the idea of relative age. More- 
over, along the great bedding planes marginal sediments were 
laid down at the same time as thalassic deposits were formed 
farther out from the shore. Therefore, as a line for the sepa- 
ration of the Coal Measures into two subdivisions, into a pro- 
ductive and a barren series, as a line which under existing con- 
ditions is of practical use in mining operations, one which also 
indicates the first marked physical and faunal changes in the 
sequence of strata in passing in a seaward direction from the 
ancient margins of the basin, the first great limestone met with 
was selected as the most reasonable, natural and convenient 
horizon. For this reason, it was stated* that in considering 
the Coal Measures as a whole, two tolerably distinct classes of 
sediments were readily recognized : (1) the marginal or coastal 
deposits, and (2) the beds laid down in the more open sea. 
These two categories are sharply contrasted lithologically, strat- 
igraphically and faunally. 
The first category is characterized by the rocks being pre- 
dominantly argillaceous shales and sandstones, with practically 
no limestones. The individual beds usually are very limited 
in extent, and replace one another in rapid succession, both 
laterally and vertically. The sandstones often form great 
lenticular masses, sometimes deeply channeled on the upper 
surface, the excavations being filled with Coal Measure clays. 
These and many other phenomena attest a constantly shifting 
shore line and shallow waters. The fossils contained are nearly 
all brackish water forms, or shore species. Remains of pelagic 
organisms are not numerous. 
On the other hand, the second class of deposits is made up 
largely of calcareous shales, with heavy beds of limestone. 
The layers are evenly bedded, and extend over very considera- 
ble distances. The faunas are chiefly composed of strictly 
open-sea forms. 
With this idea of the Coal Measures of the Interior basin, 
the limits of the two formations in Iowa and the districts to 
the south assume somewhat different lines from those which 
have been commonly recognized. 
The geological cross-sections recently made in central Lowa 
* Missouri Geol. Sur., vol. iv, pp. 80-82; Jefferson City, 1894. 
