198 T. 8. Hunt—The Decay of Rocks. 
those which are to be found either in the glacial or other mod- 
ern deposits, or lying in situ as undecaye rounded masses in 
the midst of decomposed rocks. It is difficult to resist the con- 
clusion that these rounded masses of the eozoic ages must have 
been formed under conditions not unlike those which gave rise 
to their more modern representatives. 
20. The various considerations above presented thus led 
the writer in 1878 to assign to the beginning of the process of 
rock-decay an antiquity compared with which the time that 
has elapsed since the drift-period is to be regarded as of short 
duration. It was, however, then suggested ‘by him that a cli- 
mate and atmospheric conditions unlike those of modern times 
might have favored the process in 98 earlier ages. © Further 
evidence was soon forthcoming both of the former spread of 
this tay over northern regions and of its great antiquity. 
4 I was callec to examine the condition of the great 
‘sinuel then recently opened through the Hoosac Mountain in 
western Massa hae my report on which was published by 
the General Court of the State ;” while a note on the observa- 
tions therein made which havea beari ing on the present inquiry, 
Was presented to. the American Institute of Mining Engineers. 
in on er, 1874, 
A . As there explained, the gneissic rock of Hoosac moun- 
tain, oe the west end of the tunnel, 700 feet above the sea, is 
- face anil w were partial at 1,000 feet, where it is 230 feet below; 
. while farther in, at 1,200 feet, an included bed of Le pReiie 
fiat the fsa estone. It was evident that thie reat mass. 
of decayed gneiss at the western base of Hoosac Mountain is 
a a portion of a once wide-spread mantle of similar materials __ 
#1 House Document No. 9, 1875. 
32 Proc, Amer. Inst. M. E Rogier, iii, 187. 
