ONTARIO DIVISION. 
363 
cal equivalents, and in fact identical with the red rocks overlying and interstratified with the 
upper part of the Shawangunk grit. At Townsend’s iron mine in Cornwall, the decomposed 
Delthyris shales, with their characteristic fossils (one of the members of the Helderberg 
division), are seen, and the red slates of the formation under consideration adjacent, and a 
coarse pebble rock, sometimes white, sometimes red like the Shawangunk grit, also near at 
hand in a nearly vertical position.* This locality is a mile or two northeast of the northeast 
point of Skunnemunk mountain in Cornwall, Orange county. 
The whole extent of this range of red and grit rocks, from the New-Jersey line on Bell, 
vale mountain to Townsend’s mine in Cornwall, is in a highly inclined position, often vertical; 
and the same is true of the similar rocks which are supposed to be an extension of this range 
from Fishkill through Dutchess, Columbia, Rensselaer and Washington counties, into the 
State of Vermont. 
The association of the Helderberg limestone with these red slates, grits, and red and white 
conglomerates, may be considered as very strong evidence, almost decisive, that these red 
rocks are the equivalents of those of the west side of the Shawangunk mountain, and of the 
central portions of New-York (the Medina sandstones, Oneida conglomerate, Onondaga salt 
group, and grey sandstone), instead of the red sandstones of the middle secondary of Rock¬ 
land county and of New-Jersey. 
Dr. William Horton, who made most of the detailed examinations of Orange county, men¬ 
tions the following localities of these red and grit rocks on the eastern side of the Walkill 
valley, along the base and in and near the Highlands. 
“ The same red rock is found in the town of Blooming-grove, but in a different situation 
and position. It is first found in this town on the southeast side of the Round hill. 
“ Round hill, like the Highland ranges, is primitive, and here the grit rock inclines against 
and rests upon it. The grit rock is regularly stratified; line of bearing same as in Shawan¬ 
gunk mountain, but it dips to the southeast. It passes through all kinds of composition, 
from compact to soft and slaty on one hand, to a coarse conglomerate on the other ; and all 
shades of color, from milk-white to brick-red. From the point mentioned, it extends north¬ 
east nearly four miles, until intercepted in its line of bearing by a part of Woodcock moun¬ 
tain, which is primitive. 
“ A similar rock is again found in the southeastern face of Skunnemunk mountain, and at 
its base. But here it is interstratified with the greywacke and greywacke slate ; and while 
all the colors already mentioned exist here also, there are some layers which are different. 
The pebbles of which these layers are composed are much larger, and about half of them 
are very white, and the remainder very red. All the pebbles are smooth, as if water-worn. 
“ These layers extend as far south as Skunnemunk mountain, and about two miles farther 
* Vide Plate 5, fig. 13. The diagram may not convey a very correct idea of the position of these rocks. The stratification is 
very much deranged in the vicinity, being on one of the axes of the disturbance, and the order of superposition is not considered 
£S definitely ascertained. An important question may be settled by a rigid examination of that vicinity. 
46* 
