THE GEOLOGICAL HISTORY OF NEW YORK STATE 43 
region such low knobs were not covered by the water. At this 
same locality there is a fine exhibition of coarse conglomerate 
at the base of the Potsdam sandstone, the boulders of the con- 
glomerate often ranging from one to three feet across. These 
boulders were torn off the Adirondack cliffs by the waves of the 
Potsdam sea and were deposited near shore in local depressions of 
the old rock surface. The sandstone itself everywhere abounds in 
ripple marks, thus proving the shallow water (near shore) origin 
of the rock. All the rock in the walls of the famous Ausable Chasm 
(Clinton county) is Potsdam sandstone (plate 18). 
Immediately overlying the Potsdam and showing about the same 
areal distribution, are alternating sandstones and limestone beds 
(Theresa formation) which show a thickness of from 50 to 200 
feet. After still greater subsidence, the important formation known 
as the Little Falls dolomite (limestone) was deposited, layer upon 
GRENVILLE. POTSDAM, THERESA 
BCALE: HORIZONTAL PELE, VERTICAL .>40 FEET 
Fic. 15 Section passing through North Galway in Saratoga co. and show- 
ing how the Cambric (Potsdam and Theresa) strata overlap upon a hillock 
of Precambric rock. This knob of Precambric rock stood above the general 
level of the peneplain (early Paleozoic) and was not submerged under the 
Potsdam sea, 
After W. J. Miller, N. Y. State Mus. Bul. 153, p. 5 
layer, in the Upper Cambric sea. This formation which is hard, 
compact and of light gray color, shows a thickness of several hun- 
dred feet in the gorge at Little Falls. It rests directly upon the 
Precambric rock there (see figure 7), which shows that the Cam- 
bric sea spread over that region for the first time when that dolo- 
_mite was forming. The Little Falls sea swept all around the Adi- 
rondacks, except what is now the western border from Trenton 
Falls to the Thousand islands district. Occurrence of the dolomite 
in small outlying masses at Wells (Hamilton county) and Schroon 
Lake (Essex county) proves that the Little Falls sea extended well 
into the eastern Adirondacks. Rocks of this age appear to be pres- 
ent in southeastern New York-and if so, the Little Falls sea also 
overspread that region. Direct evidence for western and southern 
