1873.] 153 [Burbank. 



It is well known that facts similar to those here noticed, have been 

 observed in many of the warmer regions of the globe. 



In Vol. ix. (p. 84), of the Smithsonian Contributions, Dr. Hitch- 

 cock, under the title of Erosion, speaks of the disintegration of the 

 rocks by aqueous and atmospheric agencies in the States south of 

 Pennsylvania. On page 94 also occurs this remark : " It is surprising 

 sometimes to see to what depth the whole character of the rock will be 

 changed, and how it will be disaggregated, so that aqueous agency can 

 easily denude its surface." Had Dr. Hitchcock fully accepted the 

 Glacial Theory of the Drift, he could hardly have failed to give these 

 facts more prominence in the discussion of the general subject. 



Among those who have more recently written upon this subject, I 

 know none who have observed so accurately, or described so clearly, 

 the phenomena of the decomposition of the rocks in place, as Prof. 

 C. F. Hartt, in his recent work on the Geology and Physical Geog- 

 raphy of Brazil. Prof. Hartt, however, finds evidence that in many 

 of the cases which he has described the decomposed rock is now cov- 

 ered by drift. This is not the case in the instances which I have 

 observed in North Carolina; but the decomposed material remaining 

 in place forms a covering over the solid rocks, averaging at a low 

 estimate twenty-five or thirty feet in depth, even among the hard 

 granitic rocks. Comparing with this the very small amount of disin- 

 tegration which has taken place among similar rocks now exposed 

 near the surface in the Drift regions, the conclusion seems unavoida- 

 ble that the time which has elapsed since the drift period must be very 

 short compared to the ages during which these solid rocks were undergo- 

 ing decomposition by chemical and atmospheric agencies. 



It may fairly be inferred that the rocks of eastern New England 

 were, before the Glacial Period, decomposed and disintegrated to a 

 very great depth; and thus the immense amount of material constitut- 

 ing the glacial drift of this region may be accounted for. 



Prof. Shaler has shown that the mass of.the drift materials must 

 have been " rent from the floor of the glacier as it moved along," 1 

 since the vast extent of the ice sheet precludes the notion of any- 

 thing like lateral moraines He does not, however, controvert the 

 generally received theory that the mass of the drift material has been 

 produced by the mechanical action of ice in grinding and wearing 

 away the solid rocks. 



3 See Proceedings of the Boston Society of Natural History, Vol. xni, p. 199. 



