G. F. Wright — Unity of the Glacial Epoch. 355 



tioned by Professor Salisbury as among the features "long 

 since recognized by Professor Cliamberlin " and which " have 

 been made use of by him and his assistants in field determina- 

 tion." (Bull. Geol. Soc. Am., vol. iii, pp. 181, 182. Also An- 

 nual Report of the State Geologist of New Jersey for 1891, 

 pp. 103-108.) Contrasting the earlier with the later drift as 

 seen at Little York, Oxford Furnace, High Bridge and Patten- 

 burg (points from three to fifteen miles south of the moraine as 

 laid clown by the New Jersey Report of 1878), Professor Salis- 

 bury says, " While the one exhibits oxidation, leaching and 

 disintegration in an advanced stage of development even to its 

 base, where it is thirty feet thick, the other has not suffered 

 oxidation and leaching on any such scale as to make them 

 apparent more than two or three feet from the surface, and 

 the softest and most easily disintegrated varieties of rock often 

 present a degree of freshness which, so far as the eye can see, 

 might characterize masses of rock worked out of their parent 

 ledges within the memory of living men. We hold, there- 

 fore, that this extra-morainic drift represents the remnant of a 

 drift covering once much more extensive and more uniformly 

 present than now, and that, like the drift in and north of the 

 great terminal moraine, it was formed by an ice sheet, but by 

 an ice sheet which overspread New Jersey much earlier than 

 that which made the terminal moraine and the main body of 

 drift, which lies north of it." (N. J. Ann. Rep. 1891, p. 105.) 

 Similar remarks are repeated in even more confident tone in 

 the Bulletin of the Geological Society already referred to. 



8. Another indication of the great separation in time be- 

 tween the first and the second glacial period, adduced by 

 Professor Chamberlin, presents itself in the extent of erosion 

 which he supposes to have taken place in the river valleys ex- 

 tending southward from the glaciated area, since the upper 

 terraces containing glacially transported material were formed. 

 (Some Additional Evidences bearing on the Interval between 

 the Glacial Epochs, Bull. Geol. Soc. Am., vol. i, pp. 469-480.) 

 In the Mississippi Yalley the upper terrace assigned by Pro- 

 fessor Chamberlin to the first glacial period consists of the fine 

 silt or loess deposited on bluffs about 200 feet above the present 

 river bottom. Between the deposition of this silt and the sec- 

 ond glacial epoch, according to Professor Chamberlin, a trench 

 about 300 feet in depth and about sixty miles wide was eroded 

 by the Mississippi all the way from Cairo to the Gulf, " with 

 corresponding erosion trenches along the upper branches dur- 

 ing the interval between the two epochs" (p. 471). In the 

 upper Ohio valley these high level terraces correspond to what 

 I had assigned to the effects of the supposed glacial dam at 

 Cincinnati. In the valleys of the Susquehanna and the Dela- 



