1913.] NATURAL SCIENCES OF PHILADELPHIA. 595 



tuff or a shale; in fact, it is of much the composition of pipe-clay. 

 This is particularly true of the layers above the lacustrine chert 

 horizon, where these virtual shales become very white and thin- 

 bedded and are hard to distinguish, when massive, from the overlying 

 marls. These are the upper tuffs of Purves, and are quarried at 

 Scotts Hill. 



When the ''volcanic sands and sandstones" are typically developed, 

 ^s at Dry Hill or at Corbizon Point, they form the base of the section. 

 They are dark reddish or purplish in color, with numerous concre- 

 tions, resembling boulders, of a somewhat harder character, and are 

 made up of volcanic sand and gravel, all water worn, with small 

 pebbles of the compact hard andesite of the igneous basement, from 

 which they are doubtless derived. They are but slightly compacted; 

 firm, but yielding readily to the pick, and crumbling easily in the 

 fingers when in detached fragments. They are overlaid by a few 

 feet of yellowish tuff conglomerate, consisting of rolled fragments 

 of a lighter color, with much green earth in minute particles, which 

 gradually passes into the impure yellowish marls with the flint 

 layers of the "lacustrine or fresh-water chert." The exposure of 

 these flinty layers at Dry Hill follows the strike of the rock for some 

 distance, and these beds at this point have furnished the following 

 section : 



Section at Dry Hill. 



5. Compact shale with plant impressions 10 ft. 



4. Hard impure limestone with two, or sometimes three, 

 layers of flint, carrying fresh-water shells; the flint layers 

 varying from one inch to four inches thick, and the fossils 

 occupying about one inch thickness in each case 2 ft. 



3. Hard impure limestone without fossil layers 2 ft. 



2. Yellowish tuff conglomerate, pebbles of tuff and andesite 5 ft. 



1. Dark reddish or purplish volcanic sandstone 18 ft.-f 



The base of the volcanic sands is not exposed at this locality nor 

 at Corbizon Point. Several small faults exist near the north end of 

 the Dry Hill exposure, one dislocates the measures about 25 ft. with 

 an upthrow to the north, and one or more must exist between Dry 

 Hill and Corbizon Point, the total upthrow to the north aggregating 

 upwards of 400 feet, as the same succession of beds is to be noted at 

 Corbizon Point as is given in the above section at Dry Hill. No 

 exposures of the rock in place can be seen along the coast between 

 Dry Hill and Corbizon Point, the beach being fiat and sandy; and 



