208 WAPPINGER LIMESTONES AND ASSOCIATE STRATA. 
tinguished from each other by the fact that P. Sarato- 
gensis has a glabella generally smaller than that of the 
other trilobite and with nearly parallel sides, a very 
narrow and simply convex front margin, very small 
eye-lobes, and no occipital spine; while the P. Calci- 
Sera has a glabella more conical in form, broadening 
posteriorly, a very broad front margin with a doubly- 
curved surface, very large and furrowed eye-lobes, and 
an occipital spine. It is instructive to note that this 
locality of Poughkeepsie Potsdam, and probably the 
Smiley strata also, are thus correlated with the Potsdam 
of Saratoga county. 
In my former paper, the Potsdam was identified as 
continuous along the western margin of this limestone 
belt to the Hudson River. The new localities above de- 
scribed lie along a line which runs close to the eastern 
border of the belt. This suggests the poSsibility that 
the main ‘width of the limestone here, of over a mile, 
may consist of folds of Potsdam strata. The litho- 
logical features are more in favor of this theory than 
against it. These Potsdam strata, along their eastern 
edge, appear, at one point at least, to be faulted against 
Trenton strata, ¢.e., on Kimlin’s farm. 
The locality on the summit of the most eastern of 
these three limestone belts, south of the MacPherson 
(formerly Boardman) place, mentioned in my former 
paper as probably Potsdam, is such, without much 
doubt. Here also these primordial rocks are in close 
juxtaposition with highly fossiliferous Trenton strata, 
which lie immediately to the east, indicating a probable 
strike-fault. 
Another very interesting locality of fossiliferous Pots- 
dam has been developed some distance further to the 
northward. It is in the main belt of the Wappinger 
limestones, almost midway between Pleasant Valley 
and Salt Point. The branch road passing towards the 
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