POST-PALEOZOIC FORMATIONS. 87 



stantly moving marginal zone, creeping inland, overlapped and 

 covered the older rocks, while farther seaward very different 

 deposits were laid down. Thus in the coastal swamps coal and 

 its associated beds were being formed contemporaneously with 

 the clays and limestones farther outward. 



In Missouri the Coal Measures have a slight general slope 

 to the northwest or west; in Iowa they dip to the west or 

 southwest. That is, they are now inclined seaward toward 

 the open sea of later Paleozoic times in the continental 

 interior. The region has doubtless undergone many slight 

 oscillations since Paleozoic times, and beds are probably now 

 considerably nearer the line of horizontality than they were 

 when originally deposited, the successive later tillings having 

 left western portions of the area relatively somewhat higher 

 than when the rocks were first formed, yet allowing the origi- 

 nal westerly direction of the dip to remain about the same. 



CRETACEOUS. 



In the blufTs of the Mississippi river, in Scott county, 

 there are certain arenaceous beds often somewhat argillaceous, 

 which, on account of lying beneath the so-called Eocene de- 

 posits of the region, have been referred doubtfully to the Cre- 

 taceous age. They are said to rest unconformably upon the 

 Silurian strata, and have overlying beds superimposed uncon- 

 formably upon them. Considerable disturbance in the regular- 

 ity of the strata is noticeable. 



In connection with the probable occurrence of Cretaceous 

 rocks in southeastern Missouri, it is of interest to know that 

 quite recently the strata of the same age have been traced from 

 the north in Iowa nearly to the boundary in Missouri, so that 

 it is not improbable that Cretaceous outliers will eventually be 

 found in the northwestern portion of the state. 



:eocene. 



The Mississippi embayment, which in early Tertiary times 

 extended northward beyond the present mouth of the Ohio, 

 appears to have reached into Missouri. The deposits which 



