10 ORIGINAL CONNECTION OF THE EASTERN AND 



Allowing foi* an erosion rate of one foot in seven thousand years, which 

 is now about the average of the Mississippi Valley, the loss of strata in a 

 million of years would be about 150 feet. Assuming that this region has 

 been subjected to erosion since the close of the carboniferous, and allow- 

 ing only this low rate of decay to the rocks, at least fifteen hundred feet, 

 and perhaps twice this amount, have gone off of the region which remains 

 between the Appalachian and the Michigan field. 



As this region north of the Ohio has been the seat of considerable 

 glacial action, we cannot expect to find evidences of the former presence of 

 the coal-measures such as we have noted in Kentucky. In Kentucky the 

 glacial sheet did not atfect more than a few hundred square miles of its area 

 in the northern part of the State, so that nearly every hill-toj:) retains some 

 evidences of the deposits that have disappeared by erosion. No such 

 relics of eroded strata can be looked for in any glaciated region. 



Accepting fifteen hundred feet as the minimum of erosion that must 

 have taken place in this district since the time of the coal-measures, it 

 is clear that the larger part of the region east of the Mississippi, wdiich 

 now has beds below the carboniferous exposed at the surface, must have 

 been at one time covered by the coal-measures. All the coal-fields from 

 Iowa, Kansas, and Missouri must have been connected together and 

 joined with the Appalachian coal-field. 



Whoever will watch the process of erosion as it now goes on upon the 

 carboniferous strata of this region, wdll easily see that the wearing away 

 of these beds goes on more rapidly than it does in any other deposits 

 of the Ohio Valley. This is shown on the topography of the district, 

 which is marked by the very deep erosion of the smaller streams. The 

 sandstones and shales above the conglomerate beds of the millstone grit 

 are singularly incapable of resisting the action of running water. The 

 streams that drain this district pour out torrents of sand in their times 

 of flood. This sand being composed principally of quartz, is easily trans- 

 ported by flood, waters. The granular character which it gives the rocks 

 of the country favors the absorption of water, which, under the action of 

 frost, breaks up the beds with great rapidity. In the coal-measures 

 there are none of those dolomitic limestones which, in the lower parts 

 of the palaeozoic beds, interpose such enduring resistance to the action 

 of water. Accepting the determinations of the erosion rate given by the 

 sediment carried by the Mississippi river, it seems to me reasonably cer- 



