GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 75 



Presumably the beds with which the bkiish beds are interstratified 

 belong with them and thc'^Beekmantown may be fairly well repre- 

 sented. Elsewhere it has not proved possible to make any corre- 

 lation even of a provisional character with this horizon. 



The Trenton. The presence of this horizon within the Fish- 

 kill limestone was first indicated on the basis of fossils by Professor 

 J. D. Dana.^ He described the white fine-grained and gray hme- 

 stones north and east of Shenandoah and announced the discovery 

 in the gray rock '' one-third of a mile north of Shenandoah Cor- 

 ners " of " large shells of a Strophomena like S. alternata, 

 distinct in form though disguised by pressure and slight alteration, 

 indicating for the beds a Trenton age." He also noted suggestive 

 forms and markings between Plopewell and Fishkill,- but nothing 

 of distinctive value was obtained. 



This horizon, as known from the Wappinger belt, was definitely 

 identified by the writer along the western margin of this limestone 

 in close association with the beds carrying O p h i 1 e t a c o m -s 

 pacta. In the second field northwest of the barn on the farm of 

 Albert Plaight, on the road from Fishkill Village to Glenham, a 

 ledge of coarse conglomerate lies just south of the ledge showing 

 the O. compacta. A few yards east of the latter ledge a 

 finer conglomerate carrying Solenopora compacta was 

 discovered. The latter is almost covered with soil and this rock is 

 exposed in only a few places. The conglomerate was also followed 

 along the edge of the wood in a series of low-lying knolls for some 

 distance. About half a mile northeast of these ledges, about 350 

 yards northeast of the Southard house, and the same distance north 

 of the public road, near the edge of the woods, at the point where 

 an old wood road leaves the woods, the light grayish- colored rock 

 passes into a thin layer of fine conglomerate of the same color and 

 then abruptly into a dark blue fine-grained conglomerate. The ledge 

 showing this transition is in place, but is very narrow and lies nearly 

 flat, dipping at a ver}^ slight angle to the southeast. A hundred feet 

 northeast of this ledge, beyond a stone wall, the coarse conglomerate 

 outcrops. What appeared to be brecciated conglomerate was noted 

 in one or two ledges farther north. 



There is thus a narrow, but well defined, strip of the Trenton 

 conglomerate along the western margin of this limestone. Its for- 

 mer eastward extension is wholly problematical. 



1 Amer. Jour. Sci. Ser. 3. Dec. 1880. 20:452. 

 2/\mer. Jour. Sci. Ser. 3. May, 1879. 17:383. 



