ONTARIO DIVISION. 
355 
South of Rochester, Ulster county, near the locality of pyritous grit, is a red shale passing 
into a red clay* by exposure to the weather. It covers the white rock in patches in this 
vicinity. The grit rock is .here waved in gentle swells, along axes of elevation which are 
subordinate to the two main axes of the Shawangunk mountains.! It is thought probable that 
beds of iron ore may be found in connection with this rock, which is highly ferruginous and 
frequently pyritiferous. Iron ore abounds in some parts of Pennsylvania and New-York in 
a similar geological position. 
The observations made do not render it certain whether these red rocks are equivalent to 
the Onondaga salt group or the Medina sandstone ; but it is thought probable, from some of 
the mineral characters, no fossils having been seen, that they belong to the epoch of the 
Medina sandstone, and that the subjacent Shawangunk grit is equivalent to the grey sand¬ 
stone instead of the Oneida conglomerate. 
2. Shawangunk! Grit or Conglomerate. 
(Formation No. 4 of the Pennsylvania Geological Reports.) 
This rock varies in texture from a conglomerate to a fine-grained grit rock, and it is almost 
entirely siliceous. It is generally white or light grey in color; but there is one bed near the 
upper part of its mass, that is fed. Most of the layers of the rock are very hard ; some are 
sandy, and others even slaty. Its colors are white, grey, greyish and reddish white, and brick 
red. 
The mountain on which the grit rock abounds has taken its name from the predominant 
color of the rock ; the word Shawangunk meaning, it is said, in the language of the abori¬ 
gines of the country, white rocks. 
The Shawangunk grit rock has been called “ Millstone grit,” by Professor Eaton; and it 
well deserves the name, both from its uses, and its similarity in texture and mineral compo¬ 
sition, to the millstone grit of England ; but as it has a different position, in the geological 
series, from that rock, which has now become a term indicating a conglomerate grit in a par¬ 
ticular geological position, I have thought it better to use a local term for this formation, viz : 
Shawangunk grit. 
The Shawangunk grit has not a very extensive range in the First geological district of 
New-York ; but in New-Jersey and Pennsylvania, it is more largely developed. It extends 
in an almost unbroken range from the New-Jersey line on the top of the Shawangunk moun¬ 
tains, to Rosendale near Kingston, a distance of forty-three miles, wheVe it disappears beneath 
* The clay beds and loams of many parts of the valley of the Rondout, and of this part in particular, are reddish, as is sup¬ 
posed from the intermixture of the materials derived from the “ red rock.” 
t Dr. Horton’s Report, in New-York Geological Report, 1839. 
t Shawangunk, pronounced by the Indians Shong-gum, meaning white stone, is very appropriate. People now living, have had 
this explanation from the lips of the Indians, 
45* 
