ARTHUR WINSLOW — THE MISSOURI COAL MEASURES. 



115 



.'!. That during the process of deposition the strata from the base to the top of 

 tin- ( loal Measures were, at intervals, at or near the surface of the water, permitting 

 the growth of the coal flora and the accumulation of coal. 



4. That at least some of the strata were deposited in an exactly horizontal 

 position. 



5. That the margin of the Coal Measures never extended much beyond the 

 limits at present recognized, and that the strata of the interior never reached over 

 those of the margin. 



According to views hitherto presented, the Coal Measures of Missouri have Ween 

 separated into upper, middle, and lower divisions, respectively 1,317, 324, and 250 

 feet thick * all having a slight dip a little north of west. The prevalent opinion 

 concerning these divisions, as well as those of the contiguous Iowa Coal Meas- 

 ures, is that they underlie each other successively, and that, should the strata of 

 the upper Coal Measures in the northwestern part of the state be penetrated by a 

 shaft, the members of the middle and lower Coal Measures would be successively 

 encountered. The reservation is generally made, however, that some of the beds 

 will probably. thin out, disappear, or he replaced by others, so that exactly the same 

 succession of strata cannot be expected, though whatever, may he included under 

 the indefinitely applied term " formation " is considered to be continuous. The 

 adjoining figure 27 represents in a general way the implied and commonly conceived 

 positions and relations of these divisions of the Coal Measures. 



Fioube :!" — Ideal Section of the Coal Measures of Missouri and Iowa. 



The nature of some of the Coal Measure strata demands horizontality of position 

 a1 time of deposition, and as, according to the above representation, the strata are 

 parallel with each other, they must, on this interpretation, all have been deposited 

 as horizontal layers and subsequently tilted simultaneously into the present posi- 

 tion. Further, the existence of coal beds near the base of this formation shows that 

 even the lowermost strata were accumulated near the surface, and hence, to produce 

 the conditions generally pictured, would require a regional subsidence of aboul 2.000 

 feet, equal in rate and amount over the whole area, with which the process of deposi- 

 tion kept pace equally and exactly overevery portion. A restoration to a horizontal 

 position of these strata is represented in figure 28, ami it is there apparent at a glance 

 that, following out this supposition, the portions of at least the upper part of the 

 formation represented could be only small remnants of the whole, and that, with 

 the indicated thicknesses, they must once have spread over the whole ( >zark region, 

 as well as over the area of lower rocks in northern h>\va. We cannot believe such 

 extension possible withoul at least some remnant of these rocks being left over 

 territory where t hey are now never found, as already stated in connection with the 



* Report Mo, Geol. Survey, 1872, pari ii, p 6. 



