HUDSON R1VP:R HKI>S near ALBANY 559* 



Tlie eastward clastic development of the Trenton is farther in- 

 dicated by the facts which have been gathered by others in re- 

 gard to the thickness and fossil contents of this Trenton in the 

 Hudson and Mohawk valley regions. As noted in the introduc- 

 tion, the fauna of the Trenton limestone has in the limestone 

 belts to the south only a lower Trenton aspect. This limestone 

 is directly followed by shales; hence the middle and upper 

 Trenton beds must either be absent entirely or be represented 

 by another facies. The possibility that the middle and upper 

 Trenton limestone had been present and subsequently abraded 

 (as the Trenton limestone conglomerate bed in the shales might 

 suggest), can be disregarded on account of the presence of middle 

 Trenton fossils in the shales. It has farther been observed by 

 Walcott (36) that at Mt Anthony (Rensselaer county), where 400 

 feet of limestone occur, M a c 1 u r e a and M u r c h i s o n i a are 

 found "nearly 200 feet below^ the shales". The Trenton limestone 

 could, therefore, at that locality reach 200 feet at the utmost,, 

 from which figure, however, are certainly to be subtracted the 

 measurements of the Black river, Lowville (Birdseye) and upper 

 Chazy limestones, which reduce this figure probably by one half. 

 In contrast to this stands the thickness of the Trenton limeistone 

 in the typical section at Ttenton Falls, where though the top 

 and bottom of the formation are covered, 270 feet were obtained 

 by Prosser and Cumings's careful measurements (56). It is a 

 highly interesting fact that, according to the figures obtained 

 by the same investigators, the Trenton limestone gradually thins 

 out in approaching the Hudson valley region. At Littlefalls only 

 104 feet of limestone was found between the Lowville limestone 

 and the Utica shale; at Canajoharie and the Flat creek near 

 Sprakers only 17 feet of Trenton limestone; at Tribeshill, 40 feet; 

 along Morphy creek between Cranesville and Amsterdam, 37 

 feet; and opposite Cranesville, 21 feet; while Y\^alcott reports 

 only 40 feet of Trenton limestone from Saratoga, north of the 

 region under consideration. 



