CHAMPLAIN DIVISION. 
383 
grit with which it is frequently associated, are supposed to belong to the group described in 
the Ontario division. 
Prof. Dewey described the principal rock of this group so correctly in his “ Section from 
Taconic range in Williamstown, to the city of Troy on the Hudson,” in 1821, that his 
description is quoted below. 
“ Greywacke. This rock begins to appeaj^ about sixteen miles east of Troy, covering the 
surface in rounded masses of very various size, and forming also vast strata rising into hills in 
Petersburgh, constituting the mountains of Grafton, and extending as the general rock through 
Brunswick to Troy. The mountains of it in Grafton are, I judge, from eight hundred to twelve 
hundred feet in height. It is, like all the other strata from Hoosick mountain to the Hudson, 
inclined to the east at various angles from ten to forty degrees ; its general inclination may 
be twenty to twenty-five degrees. It consists of quartz, cemented by a greenish argillaceous 
substance, which generally forms the principal part of the rock, and is evidently a mechanical 
deposit. The quartz is sometimes very fine, but generally is readily seen by the eye, and is 
occasionally so large and abundant that it resembles breccia. The fracture often shows the 
quartz to have been rounded masses, and in these cases the stone does not appear porphyritic. 
In other cases the stone is so very close-grained and compact, containing also felspar, that 
it might have passed for porphyry, had it not been connected with specimens that could not be 
mistaken. This rock, though quite tough in the cross fracture, readily breaks into prismatic 
fragments along its veins, which are usually filled with quartz. By the action of the weather, 
large rocks are divided into innumerable prismatic bodies. A small stream which rises in the 
mountains in the east part of Grafton, and runs westward into the Hudson below Troy, affords 
an excellent opportunity for examining the position of the rock in numerous places. Occa¬ 
sionally there appear in this rock, beds or veins of a reddish argillaceous slate, in Grafton 
and Brunswick.” 
“ Near Troy the greywacke has a much finer texture and darker color, and some of it 
takes a fine polish.* Where the greyvyacke stops near Troy, there begins a bed or stratum 
of argillaceous slate .”t 
The line of the graded road leading from Troy through Hoosick four corners to Benning¬ 
ton, offers fine opportunities for examining the strata of some of the rocks of the Champlain 
division. 
The mouth of the Hoosick also may be mentioned as a locality worth visiting by those who 
may wish to examine the rocks, and also the side of the turnpike half a mile west of Nassau 
village,I 
Prof. Eaton, in his description of the greywacke of Rensselaer county, says,j; “ This coarse 
grey rock forms the basis of more than half the county. It is perfectly insulated, and lies 
upon the argillite like a huge turtle upon the beach ; its back forming the middle and elevated 
* Vide Eaton’s Geology. 
t American Journal of Science, Vol. ii, p. 247, 248 ; and vide also Idem, Vol. viii, p. 21 and 24. 
t Geological and Agricultural Survey of Rensselaer County, 1822, p. 20, 21. 
