126 TT. B. D wight — Potsdam strata near Pough'keejpsie 



I struck a ledge of rock in the Wappinger Valley limestone 

 belt, which proved rich in Potsdam fossils. 



This remarkable locality is on an estate owned by Mr. 

 Albert K. Smiley, proprietor of the Lake Mohonk House. It 

 is in the outskirts of the city of Poughkeepsie, to the southeast. 

 It is about one mile southwest of Vassar College, 850 feet south 

 of the southwest corner of the Driving Park on Hooker avenue, 

 and about 2200 feet west of the road which passes south along 

 the east side of the same. 



The Potsdam rocks are found in a series of low hills or 

 ridges trending northeasterly and southwesterly in parallel 

 lines. The most interesting paleontological features appear to 

 be concentrated in a ridge lying at the northeast corner of the 

 group (Hill A, Plate VI). This is situated immediately to 

 the southwest of Smiley's detached barn, which is itself south 

 of the southwest corner of the Driving Park. This hill is 

 about 300 feet wide and MOO feet long ; it is mostly covered 

 with soil, the rock cropping out on each side, but chiefly on 

 the east, in a few narrow, quite inconspicuous ledges ; it would 

 never have attracted my attention but for its occurring within 

 the range of a systematic survey. 



Lithologically this Potsdam rock is exceedingly variable, 

 and all the varieties described occur within the small compass 

 of a few acres of ground. It is everywhere (so far as already 

 examined) calcareous, all its varieties effervescing with acids. 

 It is also everywhere more or less arenaceous; often conspicu- 

 ously such. Large portions of it are a tough, compact lime- 

 stone, often quite dark, and frequently filled with a conspicuous 

 fucoid-like tracery ; the weathered surfaces are often rough 

 with sand-grains. This variety passes into one which differs 

 chiefly in being fissile into more or less thin slabs; this variety 

 often alternates with layers of exceedingly thin and friable 

 shale, the folia of which are covered with loose sand as they 

 decompose. 



The rock also passes on the one hand into argillaceous varie- 

 ties represented by a smooth, fine-grained, massive argillaceous 

 limestone well exhibited on the west side of the main fossilifer- 

 ous hill ; and represented also by a very fissile and smooth 

 calcareous shale, well shown in a hill (E) which is a continua- 

 tion, in the second field south, of the above-mentioned hill. 

 Although nearly as fissile, this variety differs essentially in 

 appearance from the closely adjoining Hudson Eiver shales, 

 which are much darker, and more glazed or shining on their 

 surfaces. On the other hand, this Potsdam rock passes into a 

 very solid, massive quartzyte, the fine sand-grains of which are 

 everywhere in absolute contact, so that in appearance it is only 

 a grade less compact than the quartzyte of Stissing Mountain; 



