NEW BRUNSWICK CAVES. 
167 
to the north of the brook, and in some instances several rods 
distant from the latter, the ground shows narrow vertical rents 
or rifts, similar in character and direction to those near the brook, 
from one to two feet in width, and of unknown depth, but cer- 
tainly twenty feet or more. 'When seen by the writer, in early 
June, they were partially filled with snow. 
Reviewing these facts, it would seem probable that the pro- 
jection of rock-roofs and consequent formation of grottoes, or 
miniature caves, to which reference has been made, may best be 
explained as the result of rock decay in soft, easily disintegrated 
strata overlaid by more massive and enduring beds, the agency 
of disintegration being mainly that of frost. The same explana- 
tion would account for the resting of large blocks at various 
angles against the rock face, they being merely masses which 
have fallen as their support has been removed. But for the rift- 
like fissures, some other explanation is required, and none seems 
so probable as that they are due to differential movements 
and possibly to earthquake shocks. As to their time of origin, 
it would seem improbable that they are pre-Glacial, as otherwise 
they would naturally be completely filled with drift — a view which 
is strengthened by the overhanging projections above the caves, 
which, under the weight of a superincumbent heavy weight of 
ice, would certainly have been broken off. 
As connected with this subject, it is interesting to notice the 
evidences elsewhere observed of differential movements in the 
rocks of the millstone grit formation, and of extensive under- 
ground drainage as associated with the latter. For not only do 
faults abound, but in connection with boring operations under- 
taken for the discovery of coal, evidence has repeatedly been 
found of cavities or fissures, of considerable size many feet below 
the surface. Thus at Newcastle, Queens county, the diamond 
drill, at a depth between one hundred and two hundred feet, 
suddenly dropped several feet, and upon withdrawal was follow- 
ed by a fountain of water, several feet high, which continued to 
play for many months, and similar phenomena have been observed 
