1873.1 155 [Burbank. 



the rapid decomposition of the rock. But this explanation will not 

 apply in the case of the large boulder-like masses of granite and 

 sienite so abundant in North Carolina, nor to the boulders of similar 

 rocks scattered everywhere over the soil in northeastern Massa- 

 chusetts. 



The question will naturally occur whether the rocks throughout the 

 region described in North Carolina may not have suffered decom- 

 position to so great a depth, on account of some peculiarities in their 

 chemical composition which do not exist in the rocks of the northern 

 region referred to. To this it may be answered that many of the 

 boulder-like masses show no more evidence of rapid change now tak- 

 ing place than those of similar character in the North ; and that after 

 removing the decomposed rock to a great depth, a solid granite is 

 reached which appears as well fitted for building purposes as that 

 quarried in New England. 1 



Moreover, the phenomena of surface decomposition are far too 

 extensive over large areas, and among all kinds of rocks, to be at- 

 tributed to any local causes or peculiarities in the chemical character 

 of the rocks. 



The conclusions which have been drawn from the facts observed, 

 may be briefly summed up as follows : — 



1. The time which has elapsed since the drift period must be very 

 short compared with the previous ages during which the solid ledges 

 were disintegrated by chemical and atmospheric agencies. 



2. Boulders of the drift do not, in general, owe their rounded forms 

 to attrition by glacial action, but while still in place, assumed these 

 forms by disintegration and exfoliation. 



3. Whatever the force or agency of the drift may have been, it 

 did not produce the great bulk of the drift material by mechanical 

 action in wearing and grinding down the solid rocks, but its chief 

 action has been to carry forward and commingle the materials al- 

 ready disintegrated. 



1 Further researches into the chemical character of these rocks, and the nature 

 of the changes that they have undergone, are very desirable in connection with 

 this question, and I am glad to know that facts similar to those presented here, 

 have recently engaged the attention of our highest authority on questions of chem- 

 ical geology, Dr. T. Sterry Hunt. 



