No. 161.] 1^ 
chain, contracting in widtli and decreasing in elevation, until ihey 
are finally lost beneath the sedimentary rocks south of the Mo- 
hawk valley. At the Noses, about two miles west of Spraker's 
basin, the gneiss is seen at the base of the hills which have been 
here cut through by the Mohawk river. The banks on each side 
present nearly perpendicular faces, and consist of a calcareous 
sandstone in the upper part resting upon gneiss, which latter rock 
rises to an elevation of about 40 feet above the level of the river. 
It is here finely exposed by recent blasting for the passage of the 
rail-road from Schenectady to Utica. It is a beautiful variety of 
gneiss, of a gray color and slaty structure, and contains an abun- 
dance of elegant pink colored garnets. The river slope of the rail- 
road embankment at this point is faced with this rock. At the 
village of Little-Falls, the Erie canal has been carried through the 
primary, about two miles, nearly the whole distance of which re- 
quired blasting. The gneiss is elevated on each side of the Mo- 
hawk, leaving only a passage on each side for the canal and rail- 
road, and is here of a hard and compact texture, composed princi-* 
pally of feldspar and quartz, with but little mica. The color is 
reddish, green and grey; the strata are regular, dipping at an * 
angle of 10° to the east. The rock divides into large square or 
oblong blocks, which are broken with difficulty, and are not easily 
dressed, but are evidently of a most durable quality. We noticed 
a number of stores and other buildings in the village of Little-Falls^ 
built with this material, which, however, cannot be wrought so 
readily as the limestones which are found on each side of the 
mountain ridge. 
An interesting phenomenon may here be witnessed, calculated 
to throw light on the original formation of the Mohawk valley. 
The river has evidently been at a much higher level than it now 
occupies, and the falls must have receded very considerably through 
this hard rocky ridge, assisted by the parallel fissures, without 
which the rocks must have been far leSs destructible. Cavities, 
familiarly termed "pot-holes," worn by the rotary action of peb- 
bles in the currents of a former period, may be noticed far above 
the present level of the river, frequently three or more feet in di- 
ameter and as many in depth, the internal surface smooth, and the 
aperture, which is frequently of a diameter less than that of the 
interior, always wiih an upward exposure. We have noticed in 
the vicinity of other falls, similar water-worn cavities, and some- 
times of greater size, but not in such numberi. 
