FIVE TYPES OF EARTH-SURFACE IN THE UNITED STATES. 



309 





the surrounding mountains. I must connect with the same feature of surface-topography 

 that whole system of faults (southeast and northwest) to which the asphalt vein of Hughes 

 River and the upthrow of Marietta belong, as well as the northeast- and southwest-cleavage 

 of Western Pennsylvania, the southeast and northwest waves of East Kentucky, the 

 southeast- and northwest-faults which cross the Ohio at Henderson, and the Mississippi 

 in the Burlington region, and the long low island of ITuronian and Laurentian rocks, dis- 

 covered by James Hall, on the Minnesota lliver, in 1865. 



In fact, we see in all this the evidence of a strain or warp given to the earth-crust by 

 some force which has apparently carried down the Azoic and Palaeozoic continent under 

 water, toward the south and southeast, permitting the Cretaceous and Tertiary deposits to 

 surround and overlap them in all the Gulf States. It is this warped strain that has snap- 

 ped our northern anticlinals, and substituted for them downthrow-faults in Southern 

 Virginia and Eastern Tennessee, — the downthrow being usually to the east of the fault, 

 and amounting, in many cases, to the whole vertical distance from the Red Shale of XI 

 (Subcarboniferous) down to the Limestone of II (Lower Silurian). 



It is a pity we have none of the minute work yet published, which has been done here 

 and there along the borders of the great coal area, for it would help greatly to explain 

 the true nature of the erosive agency which has relieved an expanse of continent, amount- 

 ing to one or two hundred thousand square miles (its original limits are unknown), from 

 a superincumbent weight of Coal Measures at least two thousand and perhaps, if capped 

 with Permian measures, five thousand feet in height. It is evident from the map, that 

 the whole of this wastage (with the exception of a small section in the north, drained by 

 the Susquehanna and Delaware Pavers southeastwardly, and by the Genesee and Scho- 

 harie Rivers northwardly), has passed off into the Valley of the Mississippi ; and thus we 

 can account for a certain due proportion of the Cretaceous and Tertiary deposits of the 

 Southwest. But as these were also products in some measure of an ancient system of 

 short rivers which ravincd the eastern slope of the Rocky Mountains along a face of, say, 

 two thousand miles, — and probably also of another, similar, but opposite and shorter system 

 of more important rivers flowing from the Laurentian mountains of Canada westwardly 

 into the same Cretaceous sea, — we must not assign rashly too high a value to the subsidy 

 of deposit paid in by the coal area of the Eastern United States. 



We see also that the Cretaceous and Tertiary deposits of the Atlantic coast must have 

 had another origin. And yet this other origin could not be wholly different from the first. 

 For, as the map will show at a glance, the whole Devonio-Silurian (Appalachian) belt, in 

 front of the edge of the arborescently and westwardly drained area of the present 

 Coal Measures, has suffered a still more considerable loss of superincumbent material, 

 the whole of which loss must be represented by the semi-continental area of the flat Cre- 



