REVIEW OF GEOLOGICAL STRUCTURE. 9 
ent bands of limestone, which would certainly have shared any change pro- 
duced by acid water in the beds above and below them. 
THE WATER-LIME GROUP. 
Professor James Hall has recently made the suggestion that the Water- 
lime Group should rather be united with the Salina than with the Hel- 
derberg Group, with which it has be.n heretofore associated. There is, 
perhaps, no good reason why this formation should ever have been 
united with the Helderberg, as they have almost no fossils in common, 
and they occupy for the most part different areas, still there is apparently 
no better reason for grouping it with the Salina. It is the product of an 
epoch of submergence which followed the Salina period when the Salina 
lake was replaced by, or expanded, to form a water basin of much greater 
area, and in which the water, although still impure, both from excess of 
saline matter and of clay, was such as to permit its being inhabited by 
great numbers of a few kinds of mollusks and crustaceans. 
DEVONIAN SYSTEM. 
THE ORISKANY SANDSTONE. 
In New York the Oriskany varies from less than one foot to thirty feet 
in thickness; and is a white, or yellowish, rather coarse sandstone, 
traceable along a narrow line of outcrop from the Hudson to Lake Erie. 
It is succeeded above in Hastern New York by the Cauda Galli grit, an 
arenaceous shale full of the fucoid Spirophyton, from which it takes its 
name. A thin layer of calcareous sandstone about four feet in thickness 
rests on this in Albany county, to which the name Schoharie writ has 
been given. On the eastern margin of the continent, as well as in the 
south and west, all this sheet of mechanical sediments is generally rep- 
resented by limestones. In Canada the Oriskany Group consists of much 
the same materials as in New York, but is more cherty. 
In New York the fossils of the Oriskany are distinct from those of the 
Helderberg rocks below, as well as from those of Cauda Galli and the Scho- 
harie grits above, but in Canada West the most characteristic Oriskany 
species, such as Spirifera arenosa, S. arrecta, Rensseleria ovoides and Avicula 
arenosa, are found mingled with Favosites Gothlandica, Zaphrentis prolifica, 
Conocardium trigonale, Platyceras nodosum, and many other well known 
Corniferous fossils. These facts, joined to the entire absence of Upper 
Silurian species, seem to prove the Oriskany to be much more closely 
allied to the Devonian than to the Silurian system. 
It.is evident that the Oriskany sandstone is the record of a marked 
change in the physical condition of the region where it occurs, viz.: the 
