G. F. Wright— Unity of the Glacial Epoch. 367 



period (see this Journal, vol. exxxv, pp. 376-379) lie has cer- 

 tainly gone above the boundary of the fringe, and confounded 

 direct glacial deposits with those made by the flooded streams 

 of the period. 



At Pattenburg and High Bridge there are cuts in deposits 

 which at first look very much like true till, and they have been 

 adduced by Professor Salisbury as unquestionable, instances of 

 its occurrence at these points, which demonstrate by the oxida- 

 tion its great age. But a fact which Professor Salisbury failed 

 to notice would seem to be fatal to his theory. There is no 

 foreign material in the cuts ; at least Professor A. A. Wright 

 and I could not find any. All the fragments of the rock found 

 in them are from the strata which have demonstrably been in 

 place in the mountain, and may have worked down in the 

 course of the slow disintegration to which it has been subjected 

 since the beginning of Mesozoic time. An additional proof 

 of this is that there is a significant cessation of Medina bowl- 

 ders before reaching the north side of Musconetcong Moun- 

 tain in the vicinity of both these places. There are, it is true, 

 in the deposits many pieces of slate which are scratched as in 

 true till, and very rarely there is a bowlder of gneissoid rock 

 which shows faint scratches on some of its faces. But in all 

 these cases it is impossible to tell whether the scratching has 

 been done by an ice movement or by land slides and by the 

 slower process of " creep," which is everywhere going on in 

 the region. In both these places the mountain in close proxim- 

 ity rises several hundred feet above the deposits, and bowlders 

 are creeping down from them. Taking the whole situation 

 into view it seems far more probable that these deposits are 

 the product of the degrading agencies at work in wearing down 

 the mountain than that a northern ice sheet should have sud- 

 denly ceased to deposit Medina bowlders upon reaching the 

 vicinity of this mountain, unless the ice ceased to move any 

 farther. If there had ever been any such amount of Medina 

 sandstone mingled with local material as is found in the moraine 

 at Oxford, or at Little York, no lapse of time could have elim- 

 inated it. For this sandstone is far more enduring than the 

 slate of which there are so many fragments both at High 

 Bridge and Pattenburg. The evidence relied upon by Pro- 

 fessor Salisbury from the excessive oxidation of these deposits 

 is thus seen to. be illusory. He has misread the facts. 



8. The most weighty considerations favoring the duality of 

 the glacial period are found under the eighth head. Yet 

 it is more than possible that the apparent conclusiveness arises 

 from an incomplete comprehension of the facts which con- 

 fessedly are of a very complicated character, and but imper- 

 fectly known. 



Am. Jour. Sci. — Third Series, Tol. XL1V, No. 263.— November, 1892 

 25 



