across Mississippi, Louisiana, and Texas. 367 



it is stated that the cracks in the earth ran northeast-southwest.* 

 These disturbances were local, but occurring in a region which 

 must necessarily have been more or less disturbed since Car- 

 boniferous times, they may safely be regarded as corroborative 

 evidence. f 



Submerged pre- Cambrian. — The Appalachian mountains, 

 where they plunge southwestward beneath the Cretaceous sedi- 

 ments in central Alabama, are composed of Silurian, Cam- 

 brian and pre-Cambrian rocks (schists and granites), with 

 Carboniferous beds lying against their northern side. In the 

 area northwest of Austin, supposed to be the southwest termi- 

 nus of these Appalachian beds, the rocks are Silurian, Cambrian 

 and pre-Cambrian (schists and granites) with the Carboniferous 

 sediments resting against their north side. These Texas beds 

 plunge eastward beneath Cretaceous rocks. It is worthy of 

 especial note that this Texas area was submerged during Cre- 

 taceous times,* and that it was formerly buried beneath 

 Cretaceous sediments which have been removed by erosion. 

 From this pre-Cambrian area the Cretaceous beds now extend 

 away to the east, and it seems altogether probable that these 

 beds conceal the eastward continuation of the older rocks. 

 Naturally also the overlying rocks are thicker toward the east 

 owing to the greater depression in that direction. Thus the 

 rocks of the southwest end of the present Appalachians seem 

 to be identical with those of the pre-Cambrian area of Texas, 

 and to bear the same structural relations to the Carboniferous 

 rocks on the one hand and to those of the Mississippi em bay - 

 ment on the other. 



The structural relations of the Ouachita uplift. — I was at 

 first disposed to think the Ouachita uplift a part of the old 

 Appalachian land system, but this opinion I have been obliged 

 to abandon. The theory here put forward and the facts that 

 appear to support it throw much light on the structural and 

 physiographic relations of the Ouachita anticline in Paleozoic 

 times. Had this Ouachita anticline been an isolated one like 

 the Ozark island, then the southward Carboniferous drainage 

 would have flowed east of it very like the drainage of the 

 present time. If it had been a part or end of the Appalachian 

 system, the Carboniferous drainage would have flowed west- 

 ward through the Arkansas valley, but we should be at a loss 

 for an explanation of the phenomena of the Carboniferous 

 area of central Texas, and also for the absence from the 

 Ouachita region of the Cambrian and pre-Cambrian rocks so 



*This Journal, vol.xv, 1829. p. 36. 



f A second visit to the United States, by Sir Charles Lyell, N. Y., 1849, vol. 

 ii, pp. 112-181 ; Bringier in this Journal, 1821, iii, 20-22; Mint in ibid., 1829,. 

 xv, 366-368. 



% R. T. Hill, Bull. Geo!. Soc. Am., ii, 527 ; this Journal, vol. cxxxvii, 283. 



