THE WESTERN INTERIOR GEOSYNCLINE 153 



soon extended eastward into Henry, Johnson, Lafayette, Roy, Carroll, Linn, 

 Putnam, and Adair. When the Bevier coal bed was formed, near the beginning 

 of Allegheny time and after the deposition of 580 feet of material at Forest 

 City, some sedimentation had already taken place in all the region now occu- 

 pied by the main body of the Pennsylvanian and a fairly large area in which 

 there are now only small patches remaining. The land area had been reduced 

 to an island in southeastern Missouri, with a peninsula projecting into Pike 

 and neighboring counties and a small part of a northern land mass in the 

 extreme northwestern corner of the state. The western sea continued to 

 advance eastward while an eastern sea occupying most of Illinois advanced 

 westward. Probably by the end of Cherokee time the two seas had joined, 

 submerging practically all of northern Missouri and possibly nearly all of 

 southern Missouri also. No deposition appears to have taken place at this 

 time in the extreme northwestern corner of the state, for the Nebraska City 

 drilling shows less than 100 feet of Des Moines strata, probably of Pleas- 

 anton age. 1 



That these authors are justified in this conclusion is shown by a 

 study of the thicknesses of the Cherokee in Missouri as listed by 

 them. 2 Thus at Forest City in Holt County the thickness is 712 

 feet, while its average thickness in the counties to the eastward 

 becomes successively less and less, viz., Livingston 450, Linn 260- 

 310, Macon 175, Audrain 75. To the southeastward a similar 

 relationship is shown, thus: Buchanan 530, Platte 555, Clay 460, 

 Jackson 430, and Johnson 220-350 (see Fig. 2). 



The influence of the basin upon the thickness and character 

 of the post-Cherokee stages of the Pennsylvanian is not so obvious. 

 The writer, after a careful study of all the available data, including 

 deep- well and drill records from various parts of the area, has not 

 been able to find any consistent variation in the thickness and litho- 

 logic character of the formations in tracing them from the center of 

 the basin toward its margins. Nevertheless, the, lack of relation 

 between these deposits and those of the Illinois field suggests that 

 the basin persisted and that its gradual though interrupted sub- 

 sidence made possible the deposition of the Pennsylvanian forma- 

 tions of this province. It is believed that the original relations 

 have been masked in large part by disconformities within the Coal 

 Measures, several of which have been recognized, and by post- 

 Pennsylvanian erosion, which has almost entirely removed the mar- 

 ginal facies of all the formations younger than the Cherokee. 



1 Op. cit., p. 209. 2 Op. cit., pp. 39-40. 



