Crosby.] 368 [January 21, 
volcanic glass. The fragments, as we would expect,! are no longer 
voleanic glass, but quartz, which is the product of alteration. The 
brecciated rock is an old rhyolitic tufa, perodite, and it is remark- 
able that these peculiar forms have been preserved, when we 
consider the alteration to which the rock has been subjected. 
These facts are valuable not only as evidence in favor of the truly 
eruptive character of the felsites, but also as showing the similarity 
between ancient and modern volcanic products. 
DIstoRTED PEBBLES IN CONGLOMERATE. 
By W. O. Crossy. 
Under the above heading I wish to present, first, some obser- 
vations that may stand as a rejoinder to the remarks of Mr. Wads- 
worth, made at a recent meeting of the Society, during the discus- 
sion which followed the reading of my paper “ On the Evidence of 
Compression in the Rocks of the Boston Basin ;”? and, second, to 
describe the altered conglomerate in the town of Bellingham in this 
State. 
The paper referred to, as will be remembered by many present, 
was devoted mainly to a description of the pebbles in a ledge of pud- 
dingstone, in the Brighton district of Boston. 
Although Mr. Wadsworth seemed to argue against the deforma- 
tion of pebbles in general, still it was chiefly to the conclusions 
drawn from the phenomena presented at this ledge, that he took 
exceptions, and consequently my reply is properly restricted to the 
same limited locality. 
One point upon which, as it seems to me, considerable stress may 
fairly be laid, and which Mr. Wadsworth did not offer to explain, is 
the fact that the most of the indented surfaces of the pebbles, sup- 
posing them to be the effects of pressure, require pressure in a uni- 
form direction ; 2. e., perpendicular to the stratification, and in pre- 
cisely the same direction that pressure is required by the cleavage in 
the slaty layers of the puddingstone, by the fractured pebbles, which 
abound in this ledge, and by the cavities which appear between the 
fragments, and at the ends of many of the pebbles. I judge that no 
one will deny that the cleavage, fractures, and cavities must be the 
result of heavy pressure ; and yet, not to deny this, is equivalent to 
1 See paper referred to in note 3, ante p. 359. 
2 Proc. Bost. Soc. Nat. Hist., xx, 308. 
