THICKNESS OF COAL MEASURES. 85 



northwestern portion of the state, and the lower rock crops 

 out along the margin to the east. 



The estimated maximum thickness of these Coal Measure 

 rocks is about 2000 feet. That is, to penetrate the entire sec- 

 tion of these strata at a point in the northwestern corner of 

 the state, a shaft 1900 feet deep would be necessary. East- 

 ward from such a point the thickness of the underlying rocks 

 constantly diminishes, owing partly to the westward tilting of 

 the strata above referred to, and partly to the conditions under 

 which these strata were deposited, which is elsewhere dis- 

 cussed. Therefore, the thickness of this formation at any 

 point within the area of its distribution may be anywhere from 

 to 1900 feet. 



Thus, along the margin, the Coal Measure formation may 

 be considered to taper to a feather edge, while in the extreme 

 northwestern corner of the state it has an aggregate thickness 

 of nearly 2000 feet, and consists of more than 200 strata. 



On the basis of the figures recently given, there is an ele- 

 vation of about 200 feet for the floor of the Coal Measures at 

 the margin near Sedalia, and in the extreme northwest the ele- 

 vation of the floor is about minus 700 feet; the consequent 

 present slope of this floor is 1600 feet in a distance of some 150 

 miles, which is equivalent to about 10 feet per mile, or about 

 one-tenth of one degree, which is almost horizontal. The eleva- 

 tion of the surface of Maryville is about 1200 feet, so that the 

 thickness of the Coal Measures there, above the level of 

 Sedalia, is only 300 feet. 



Among the most noticeable features of the stratigraphy of 

 these Coal Measures is the variability of details. Strata are 

 characteristically non-persistent, both as regards thickness, as 

 well as material. 



According to views usually presented, the Coal Measures 

 of Missouri have been separated into an upper, middle and 

 lower division, respectively 1317, 324 and 250 feet thick,* all 

 having a slight dip a little north of west. The common con- 

 ception regarding these divisions is that they underlie each 



* Missouri Geol. Sar. parti, p. 6, 1872. 



