CLARK: TRENTON LIMESTONE AT MARTINSBURG. O 



the layers are made up almost entirely of fragments of shells, a sort 

 of coquina, while others are nearly or quite devoid of fossils. 



The peculiarities of the distribution of fossils in these strata are 

 as follows : — 



At seventy feet above the base of the Trenton there is a layer, 

 exposed on the road from Martinsburg to East Marti nsburg, which 

 contains great numbers of Sinuites cancellatus (Hall). 



One hundred feet above the base there is a layer containing, among 

 other fossils, Dalmanclla rogata (Sardeson), Isotelus gigas DeKay, 

 Calymene senaria Conrad, Cryptolithus tcssellatus Green. 



This layer is foimd near the base of the upper of the three falls 

 which have been developed by Roaring Brook in the lower part of 

 the Trenton, and five feet above the broad flat platform which extends 

 from the top of the middle fall to the base of the upper one. The 

 layer containing Crj^tolithus is only a few inches thick, and is a 

 fairly pure, nearly black limestone. Cryptolithus is quite abundant 

 and its discovery here is of considerable interest as it has not previously 

 been reported in the Trenton north of Trenton Falls in the region 

 west of the Adirondacks. 



In the strata 100 feet above the base Platystrophia first becomes 

 abundant, and the fifteen feet above the 165 foot level contain espe- 

 cially well-preserved specimens. Associated with the Platystrophias 

 are the other common fossils of the Trenton, such as Calymene senaria, 

 Dalmanella rogata, Pledambonites sericeus, etc. 



Between the 200 and 300 foot levels the limestone is composed of 

 httle else than fragments of shells, and at 280 feet is the lowest layer 

 of coarsely crystalUne limestone. Large specimens of an undescribed 

 Dalmanella are found in this stratum, and as usual, only the matrix 

 and not the fossils is affected by the crystallization. At 290 feet 

 there is a layer showing the so-called "giant ripple mark," the crests 

 being several feet apart, and their^ direction about N. 45° E. The 

 rock is composed of columnals of crinoids and fragments of brachio- 

 pods. In the hundred feet of beds just described there are no very 

 remarkable fossils, but it is the zone of the greatest development of 

 Prasopora simulatrix, which is there very common indeed. 



Between 300 and 390 feet above the base the rocks are a rather 

 coarsely crystalhne limestone which is neither very well exposed nor, 

 apparently, very fossiliferous. In the basal layer I found a Carneyella, 

 the first representative of the Agelacrinitidae to be reported from the 

 Trenton of New York; and this layer is also the lowest bed in which 

 Rafinesquina deltoidea is found. 



