438 THE JOURNAL OF GEOLOGY. 



this subsidence the Columbia formation was deposited. Some of its 

 characters are similar to those of the Lafayette, and indeed the latter 

 deposit may often be mistaken for the earlier, where unconformity is 

 not apparent. The Columbia formation covered the lower half of the 

 coastal plain, and partly filled the great valleys which thus became 

 estuaries. These deposits form the " second bottoms " of many of the 

 coastal rivers, particularly on the Gulf slope. In short, the Columbia 

 formation of the South is largely the Lafayette made over, though in 

 the North its materials grade into those of the glacial period. 



Following the Columbia submergence the continental margin again 

 rose, even to an altitude above that of modern times, to such an extent 

 as to permit of the clearing out of the valleys to a considerable extent ; 

 including those now submerged along the oceanic plateau. Then fol- 

 lowed a subsidence to modern conditions. This post-Columbia eleva- 

 tion did not last nearly so long as the post-Lafayette, for 90 per cent, 

 of the accumulations still remain. 



The altitudes at which the Lafayette deposits are now found 

 vary. In Maryland they occur at 500 feet ; southward they decline 

 so that, at Hatteras they occur at 100-200 feet. Along the axis of 

 greatest oscillation in South Carolina the formation rises to 800 feet, 

 but again descends southward so that north of Mobile Bay they rise 

 only 500 feet above tide. Again in Illinois and Arkansas, the loams 

 rise to only 350 and 250, whilst they culminate at 1,000 feet along the 

 Rio Grande. But as river terraces of the streams emptying into the 

 Lafayette sea, the reviewer has met with the extension of the formation 

 in the southern Appalachian at 1,500 to 2,000 feet, thus supporting the 

 author's conclusions as to the greater magnitude of terrestrial undula- 

 tion in the mountain regions than along the coast. 



At Cape Hatteras, the Columbia deposits now rise only 25 feet 

 above tide, but they increase to 300 feet in altitude to the north and 

 again southward, so that in South Carolina they rise to 650 feet. 

 Again they decline to 25 feet above the Gulf in Mobile Bay. Farther 

 southwestward their present elevation is from 100 to 200 feet. 



The meager flora of the Lafayette has both Cretaceous and Pleisto- 

 cene features, and the more meager fauna represents the entire 

 Neocene. The Columbia is regarded as the earliest Pleistocene, and 

 the Lafayette as the later Pliocene, though the author groups it with 

 the Miocene and small areas of marine Pliocene, the whole making the 

 American Neocene. Its biological relations are not known ; it is by 



