120 PROCEEDINGS OF WASHINGTON MEETING. 



From the actual connection between the Missouri coal fields and those of Iowa, 

 Kansas, and Arkansas one would expect to find similar conditions there, and such 

 indeed is the case. Hall,* in describing the Iowa Coal Measures, says: "We must, 

 therefore, be prepared to find ultimately that the Coal Measures, or at least the 

 productive portions of that formation, thin out in great part or entirely in that 

 direction [toward the interior], while the calcareous port ions, which are of marine 

 origin, will be found increasing in force." C. A. White f describes the shallow seas of 

 the Coal Measure period as ending well south of the northern line of the state, and 

 refers to the thickening of the formations toward the center from the border,! 

 though he is of the opinion that " the coal-producing strata passed entirely beneath 

 the unproductive ones and do not disappear by thinning out as they do in the 

 opposite directions." $ Keyes, in writing of the stratigraphy of the Iowa Coal 

 Measures, described the gradation of shales into sandstones on the one hand and 

 into coal on the other. || The coals, he says, are not in continuous layers over the 

 wdiole area, but in lenticular patches;^ and he estimates them of little value for 

 general coiTelation. 



Similar conclusions may also be drawn from the phenomena of neighboring 

 regions. Thus, Newberry, in describing the Coal Measures of Ohio, states that 

 the upper coals never reached so far as the lower ones, as they have been found 

 only in the center of the basin.** He also refers to the great variation of the 

 intervals between coal seams, and in general terms suggests an unequal sinking of the 

 area in explanation. He also described the coal basins there as of limited extent.ff 

 Orton, in writing later of the Ohio coals, states his opinion that the later coal beds 

 never extended over the outside margins of the earlier swamps, and in explana- 

 tion be suggests a simultaneous rise of the border and a sinking of the interior.! t 

 All coals below the Freeport, and others, he states, were apparently formed as 

 marginal swamps, and, with reference to the general question, he concludes : " If 

 we see reason to believe that these lower seams originated in marginal swamps. 

 with the sea near at hand, then, of course, we abandon the older view that 

 the coal seams extend indefinitely toward the center of the basin. . . . We 

 should expect to find the interior of the basin filled with terrain mort." \ \ 



I. C. White, in his recent description of the stratigraphy of the bituminous coal 

 fields of Pennsylvania, Ohio and West Virginia, states that though valuable coal beds 

 are found in the central portion of the trough, it is t rue, as a general law, that the coal 

 beds of this series (the lower Coal Measures) are thicker and better and more 

 numerous around the margins of the Appalachian field than toward the center, and 

 he states the same concerning the coals of the Pottsville conglomerate. || || 



As early as 1872, J. J. Stevenson, in describing the upper Coal Measures of Ohio, 

 Pennsylvania and West Virginia, referred to the disappearance of strata and the 



* Report Iowa Geol. Survey, 1858, part 1, page 135. 



t Report Iowa Geol. Survey, 1870, vol. 1, page 227. 



t Op. Cit., p. 250. 



gOp. cit., p. 259. 



|| The Stratigraphy of the [owa Coal Measures: Bull. Geol. Soc. Am., vol. 2, p. 282. 



If Op. cit., p L'sl 



** Report Ohio Geol. Survey, neology, vol. i, 1874, p. 117. 



tfOp. Cit., p. 1GG. 



% % Report Geol. Survey of Ohio, L884, Economic Geology, vol.5, p. 135. 



fJgOp. cit., p. 137. 



[| |! Bulletin 1 T . S. Geological Survey, no. G5, 1801, pp. 100, 181 



