34 Miscellaneous Notices of American 
Glenn’s Falls, as described by you, bear to some detached 
rolled masses lately found in this neighbourhood, about forty 
feet below the surface. ‘These pieces were thrown out in 
digging a well on the side of Prospect hill, about one mile. 
from the river.—This city is built on a foundation of argil- 
laceous marl lying in horizontal strata, and containing a con- 
siderable portion of sulphate of magnesia. In front of the 
principal street there is a steep bank composed of silicious 
slate, which rises about seventy feet above the surface of the 
river : as you recede from this, the ground declines ten or 
fifteen feet to Market square, from whence there is a gradu- 
al ascent for about one mile to the base of Prospect-Hill, on 
the north-west side of which this well was commenced 
at an elevation of about one hundred and seventy feet. The 
well was sunk about eighty feet, passing almost entirely 
through a solid mass of hard clay, (or pan,) not stratified, 
and containing rounded pebbles of quartz, &c. and rolled and 
water-worn pieces of limestone abovementioned, aspecimen 
of which accompanies this letter, and is quite different from 
any thing of the kind in this district of country.—From the 
mouth of the well the hill rises about one hundred and eigh- 
ty feet, with an uniform smooth surface, and falls off gently 
on the south-east, toa low meadow, which divides it from 
the north end of Becraft’s mountain, so called. This is a 
solid mass of grey reck supporting a blue compact limestone: 
the upper strata of both rocks contain a great variety of pe- 
trifactions which have been described by Mr. Eaton and 
others. Prospect-Hill, on the contrary, presents no ap- 
pearance of rock strata whatever, although on the surface 
and in the vicinity are found pebbles and rounded masses of 
quartz, granite, gneiss, &c. Among the pebbles we find 
slate of several colours, chlorite, jasper, basanite, &c.; these 
are also found in connection with a grey sand, which is ta- 
ken from the adjoining vallies for building purposes, and 
which is evidently composed of the particles of disintegrated 
primitive rocks, and presents so strong appearance of alluvi- 
al deposition as to be apparent to the most careless observer. 
{t appears therefore evident that this alluvial matter has 
been borne down by the rushing waters from its original 
situation in the primitive regions of the north, and deposited 
in its present location. The investigation of this subject 
appears to me of some importance in a geological view. If 
