REVIEWS. 437 



coastal plain, except at two or three localities. The topography of all 

 of these formations was greatly modified by erosion during interven- 

 ing periods of high level of the land, but in general, the successive 

 formations were planed, nearly to base level before the succeeding 

 deposits were laid down. This was the condition before the Lafayette 

 epoch, and the seaward slope of the country was more gradual than 

 at present, although the continent was high enough to allow the 

 submerged continental shelf to be a sub-aerial plain. Then came 

 the extensive subsidence and seaward tilting, which allowed the 

 invasion of oceanic waters over the coastal plain, so as to permit of 

 the deposition of the loams even upon the margin of the Piedmont 

 plateau. This subsidence was unequal, least in the region of Cape 

 Hatteras, greater along the South Carolina axis, again diminished in 

 the Gulf region, and greatest along the Rio Grande. The author 

 regards all of these Lafayette deposits as having accumulated at sea 

 level from the land wash brought down by the rivers. Although 

 devoid of marine life, so far as known, this seems the most rational 

 explanation, although the physical characters are very different from 

 those of the earlier Tertiary or Mesozoic deposits, which were laid 

 down after submergence with less decided seaward tilting. 



Mr. McGee regards the duration of the epoch of subsidence as 

 short. The succeeding elevation, which carried the country from loo 

 to i,ooo feet above tide, he regards as much longer. This uplift 

 was not uniform, probably only 100-300 feet at Cape Hatteras, and 

 1,000 feet at the mouth of the Mississippi,- but in undulations such 

 as characterized the previous subsidence ; where the greatest depres- 

 sion had taken place, there the greatest elevation followed along the 

 same axes. Moreover, it is apparent from the intensity of erosion that 

 the elevation was greater along the Appalachian and Cumberland 

 plateaus than along the coast, giving greater slope to the rivers than at 

 present. This elevation was unquestionably of long duration and the 

 erosion enormous, removing from the valleys a large proportion of 

 the accumulations of the preceding epochs and cutting through them 

 to depths of 150 feet and upward, and to widths of 10 and 20 miles, 

 even 100 miles in the case of the Mississippi. This the author empha- 

 sizes, giving great prominence to the geomorphy from which the 

 post-Lafayette elevation is deduced. 



After this long-continued period of degradation, the continent 

 subsided, but not so much as during the Lafayette days, and during 



