WILLIAM B. DWIGHT. 141 
and characteristic fossils, as encrinal columns, Lepfwena sericea, etc. The terminal bluff at 
the river is composed of both formations, the fault running along its summit, but near the 
northwestern edge. As the extreme southwestern point of the bluff is reached, the line of 
fault drops down its northwestern side, and the shales at last disappear, leaving the point in 
possession of the limestone. After careful examination I am satisfied that some, if not all, 
of the moulding sand is produced by the decomposition of the arenaceous Potsdam. In- 
deed, the process may now be seen going on in the layers of sandy limestone. It is very 
probable that the Potsdam may now be further traced across the Hudson river somewhere 
near Marlborough. 
In plate I will be found a small map showing the entire extent of the fault above de- 
scribed. 
It is proper to state here that I have strong reason to suspect the presence of a parallel 
belt of Potsdam limestone, more than amile to the east of the present one, in the most 
eastern of the three belts of limestone. The particular locality which has furnished 
‘grounds for the above statement is on the summit of the ridge about half a mile southerly 
from the mansion on the MacPherson (late Boardman) place. The rock corresponds closely 
in its lithological characters with that of the Smiley locality. I have found here but a single 
fossil—about half of one valve of a brachiopod, which, as far as it goes, corresponds per- 
fectly with Lingulepis pinniformis. I believe it to be this fossil, and that consequently the 
rock is Primordial, but cannot say that the evidence is absolutely conclusive. 
EXPLANATION OF PLATE. 
A, Hill of fossiliferous Potsdam on Smiley’s farm. 
B, Hill of Potsdam, partially conglomerate, on Smiley’s farm. 
D, C, Extensions of hill B. D is largely conglomerate. 
E, Hill containing much fine-grained, blue, thinly fissile calcareous shale of the Potsdam 
group ; a few specimens of Lingulepis pinniformis have been found here. 
¥F, Calcareous quartzyte, Potsdam group. 
The lane between the wall and fence just south of the hills E and F is the southern bound- 
ary of Mr. Smiley’s farm; at present date no Potsdam fossils, except stromatocerium, have 
been found in this belt south of this line. 
G, One of the best localities for inspecting the Potsdam limestone and calcareous shale 
composing this long hill. Stromatocerium is found here. From the summit of this 
hill a good view is presented of the wide plain of Hudson river shale which extends 
westward from its base. 
H, A small quarry of arenaceous limestone apparently Potsdam, in the field belonging to 
W. 5S. Johnston, 
I, A high ridge of light and dark-colored limestones, well exhibited at the spring here indi- 
cated ; horizon of the rocks doubtful. 
K, Outcrops of Hudson river shale at the surface of the ground within a few feet of the 
Potsdam hill B. 
L, Small quarry of compact, gritty layers of the Hudson river group, dipping at a low angle. 
O, Hilly outcrops of Hudson river shale in field north of the driving park. 
M, (In smali included map), moulding sand and dock. 
7, (In small included map), outcrops of fossiliferous Trenton on the eastern margin of this 
limestone belt. 
FEBRUARY 10, 1886—FORTY-FOURTH REGULAR MEETING. 
Charles B. Warring, Ph.D., chairman, presiding. 
The following paper was read : 
25 
