130 JT. B. D wight — Potsdam strata near Poughkeejysie 



With regard to the eastern boundary line of this strip of 

 Potsdam nothing definite can be determined from present data. 

 There are no fossils to indicate the points of transition to the 

 Calciferous and Trenton, which doubtless lie in abundant 

 development to the east. The uncertainty is increased by the 

 fact that a great part of the rock is deeply buried under drift. 

 Thus, at the northern extremity, east of the fossiliferous Pots- 

 dam, after about six hundred feet of strata (which are probably 

 to some extent at least of the same group), the limestone 

 entirely disappears under a large hill of more than fifty feet 

 depth of drift in A. Vanderberg's farm. (This hill is so 

 covered with debris of Hudson River shale that one might 

 readily suppose it to be the rock in place.) The limestone 

 does not reappear until the southeastern base of Richmond 

 Hill on Casper Creek is reached. That this eastern margin of 

 the belt is Trenton is proved by a distinct outcrop of fossil- 

 iferous Trenton filled with Solenopora compacta ( u Chcetetes com,- 

 pacta") appearing in a small patch on a hillside 520 feet from 

 the house of R. J. Kimlin on a course of 1ST. 101° E. The 

 Calciferous is doubtless extensively represented between the 

 Trenton and the Potsdam, but this has not been paleontologi- 

 cally determined. 



In view of the above facts, I can make only the general 

 statement that the minimum width of the belt of Potsdam 

 strata, measured on the surface of the ground, is somewhat 

 over 600 feet. If, as seems probable, there is at least one 

 compressed fold, the actual thickness of the deposit must be 

 over 300 feet. 



It is my present impression that the Potsdam folds occupy, 

 as indicated on the accompanying map, a strip of about 1400 

 feet in width, and that the high and continuous limestone hill 

 (K) on the east of this strip may form the western margin of 

 the Calciferous strata. In this case the small quarry in the 

 field of W. S. Johnston, at the southeastern portion of the dis- 

 trict (H), would be near the eastern edge of the Potsdam. 

 This view is strengthened by the fact that lines of ponds and 

 springs exist conspicuously along the base of this long eastern 

 hill, indicating a possible break or slip between strata along 

 this line. But as fossils have not yet been found in the last 

 mentioned hill, nothing more positive can be asserted in this 

 connection at present. 



A brief description may now be given of the paleontological 

 features of these strata. 



In the fossiliferous hill above described (A), organic remains 

 are found chiefly on the eastern side near the summit in the 

 southern half, though not in the oolytic portion. They occur 

 both in the solid fissile limestone, and in thin layers of shale 



