Scudder.] 182 [October 6, 



region west of the Mississippi is, as a whole, wearing at only about 

 one half the rate of the region east of that belt. If this is continued 

 for only ten millions years, the effect will be to make a great differ- 

 ence of the height of the two regions. 



Mr. S. H. Scudder exhibited a series of post-pliocene fossils 

 from the bluff at Sankoty Head, Nantucket, with samples of 

 the sands in which they were found, and of the underlying 

 gravels, sands and clays. 



The sands and gravels rest at base upon a thick bed of light brown 

 sandy clay of uncertain thickness, but extending upward to about 

 twenty feet above the sea-level. As the beds which rest upon it dip 

 to the southwest, and as the anchor brings up clay from Sankoty 

 Head eastward for half a mile, this clay bed is probably of great 

 thickness. Messrs. Desor and Cabot, who gave the first account of 

 this deposit, 1 speak of it as "nearly twenty feet" in thickness, but 

 as that, by their estimate of the height of the bluff and the strata of 

 which it is composed, brings the bottom of the bed exactly to the 

 level of the sea, they apparently do not intend to limit its lower level 

 to that point. In my excavations I penetrated it for over seventeen 

 feet; it was very compact and difficult to dig through, and varied 

 only, and that irregularly, in the amount of sand intermixed with 

 the clay. 



This brown clay is overlaid by four feet of gravel and coarse sand, 

 the coarser parts mostly confined to three or four inches of the upper- 

 most levels ; the upper bed is more or less ferruginous, and hardens 

 on exposure into a rather compact conglomerate. To this stratum 

 must doubtless be referred a single specimen of a bivalve (probably 

 a Mactra), with valves half open, picked up on the bluff, imbedded 

 in a lump of gravel conglomerate, and, like it, strongly oxydized. 

 The gravel is followed by about four feet of sands, subdivisible into 

 separate beds, viz.: at base, an inch or two of a very fine loose white 

 sand; followed by nearly two feet and a half of a little less fine, 

 closely packed, white sand, with irregular ferruginous streaks through 

 its mass; this is covered by nine inches of a coarse beach sand, with 

 a still coarser sand in pockets; and this again by nine inches of a 

 very fine white sand. Above this comes a foot of ferruginous sand, 



x See Quart. Journ. Geol. Soc. Lond., v, 340-44; also these Proceedings, m, 79- 

 80 ; and the Memoirs of this Society, I, 252-3. 



