4 bulletin: museum of comparative zoology. 



successfully than the rather thinly bedded Trenton limestone above it, 

 so that a platform a quarter of a mile wide has been excavated upon 

 its surface. Since the surface of this platform, even in the stream 

 bed, is more or less masked by debris from the bluff behind it, the 

 exact contact with the Trenton is seldom seen. Fortunately, how- 

 ever, I found on my second visit that the spring freshets of 1917 had 

 removed a part of the covering of detritus in the stream bed, so that 

 the basal twelve inches of the Trenton was clearly shown. This 

 proved to be a dark blue, fine grained dense limestone, mostly without 

 fossils, but with here and there a thin band of small specimens. This 

 bed was without shaly partings to divide it into subordinate layers, 

 and showed no trace of clastic matter, so there was no evidence of a 

 "basal conglomerate." It differed from the underlying Black River 

 limestone in being finer grained with a more flinty fracture, and in 

 lacking the chert. The few fossils obtained from it are species char- 

 acteristic of the Trenton, Triplecia extans being the most important. 

 Above this basal layer there would seem to be about five feet of 

 strata concealed, the next outcrop being in the bank of the stream 

 about halfway across the shelf. At this locality a few thick beds of 

 highly fossiliferous dark blue impure limestone are exposed, with 

 rather thick bands of shale between the beds of limestone. The 

 following were the most common fossils, the first three being particu- 

 larly diagnostic, and, in this section, apparently confined to the lower 

 ten feet of the Trenton : — 



Triplecia extans (Emmons), T. cuspidata (Hall), T. schucherti, sp. 

 nov., Parastrophia hcmiplicata Hall, Rafincsquina altcrnata (Emmons), 

 Suhulites elongahu Conrad, Honnoioma trentonensis Ulrich & Scofield, 

 H. bellicincta (Hall), Streptelasma corniculum Hall. 



The last species was particularly abundant; one slab, about thirty- 

 six square inches in area, containing about forty specimens on its 

 surface. From the partings between the beds of limestone, large 

 numbers of complete specimens of Triplecia, retaining both valves, 

 were obtained. 



Above the fossiliferous basal beds there are about 280 feet of dark 

 limestone in beds two inches to a foot in thickness, separated by 

 partings of shale which become more numerous and thicker in the 

 upper part of this division, but which seldom contain any great nuia- 

 ber of fossils. Some of the beds of limestone are composed of fine 

 grained material, while others contain a certain amount of more 

 coarsely crystalline calcite. In the latter case the crystalHzation 

 affects only the matrix, and does not obscure the fossils. Some of 



