184 
GEOLOGY OF THE FIRST DISTRICT. 
been observed in a northwardly direction from their original position, but almost uniformly 
are found in a southwardly direction, this inference necessarily followed. 
Westchester county is almost covered by the drift deposits, though perhaps few counties 
show rocks in place more abundantly. The boulders can almost all be referred to the parent 
sources at no great distance, in a northwardly direction. At Peekskill, these deposits may 
be seen well developed. The small stream has excavated a valley in the boulder and gravel 
beds between the village and landing, from fifty to one hundred feet deep. 
In Putnam and Orange counties, a great variety of boulders, pebbles and erratic blocks 
are found. In the mountains the boulders are mostly of the same rocks as those of the vicinity 
in a northwardly direction, except on the northern flanks of the mountains, and in the 
deeper valleys, where the rocks from a great distance to the north abound. In the valley of 
the Croton, which communicates on the north with that of Oblong creek, through the Dover 
and Ancram valley, many of the boulders are of the talcy slate containing quartz veins, like 
that of Taghkanic, Hillsdale, Austerlitz, Chatham, Canaan and New-Lebanon. The Fish- 
kill and Coldspring valley contains boulders and pebbles of all the varieties of the Hudson 
slate rocks, and the Taghkanic series that occur in the Hudson and Champlain valley, as far 
north as Whitehall. The Potsdam sandstone is the hardest of these rocks except quartz, and 
the pebbles of these two rocks are most abundant. The Potsdam sandstone pebbles are like 
the sandstone of Whitehall and Fort-Ann, and the quartz is mostly like that in veins in the slaty 
rocks in Hillsdale, Taghkanic, Canaan, Austerlitz, Chatham and New-Lebanon, in Columbia 
county; being generally white milky quartz, frequently containing chlorite, brown spar, and 
sometimes carbonate of iron, carbonate of lime, and quartz crystals. The brown spar is 
frequently decomposed, leaving earthy oxide of manganese in the cavities. The aspect of this 
quartz, together with the association of minerals, is so peculiar, as to leave no doubt of the 
parent source of these pebbles. 
The valley of the Hudson river through the Highlands, shows boulders, blocks and pebbles 
of all the rocks of the Hudson and Champlain valleys, and of the Mohawk valley, that would 
not easily grind up by attrition. They occur from the level of the river to a height of about 
a thousand feet, and some few perhaps are found higher: but they are very rare above that 
height, and are most abundant at an elevation of three hundred to five hundred feet.* The 
plain of West-Point, which belongs, in part at least, to the drift, is an instructive example of 
these deposits. In the gravel, pebble and boulder beds at that place, a person may collect a 
suite nearly complete of all the rocks, and many of their minerals and fossil remains, that are 
found in place for a distance of two hundred and fifty miles to the north. Primary rocks like 
those of the Highlands, consisting of granite, gneiss, sienite, hornblende rock, hornblendic 
gneiss, granular limestone, verd antique and augite rock, are most abundant. The rocks 
belonging to the Hudson slate group, as hard grey grits, such as have been called grey- 
wackes, often traversed by veins of quartz, and sometimes by those of calcareous spar and 
These heights are estimated by the eye, not measured. 
