i-LUKA Ul" OLDKR I'UTU.MAC FUK-MATlU.N. 383 



The pilch or (loop ravino, at tho Ixittoin of wliich thoro is ruiiiiin<j: 

 water, with a 8])riii<ii; noai- iho plant locality, niakos southwaixl. On tho 

 loft or oast hank thoro is a fine oxposuro consistinj; chiofiy of Rappahan- 

 nock sand, hnl with clay soams, and in ono of thoso, a foot aljovo tho 

 stream hod, fossil jjlants woro found in abundance*. Thoro is also much 

 lignite, and this extends below tlie bottom of th(> i-avino. A short (hs- 

 tance below the principal plant l)ed is a bhiff of typical cross-bedded 

 Rappahannock sand. Well up in tliis Ijluff, about 20 foot above the 

 stream 1)0(1, is a tliin vein of fine l)uff-colored cla\- containing abundant 

 remains of coniferous twigs with small cones and male aments, seeds, etc. 

 A bivalve shell was also foimd her(\ \ lathei- large collection was 

 made at both the horizons. These plants are fully treated in a later 

 part of this paper (see pp. 509-515). 



On May 14, assisted by Mr. William Hunter and Mr. \'ictor Mason, 

 I made a much larger and better collection than any of the previous 

 ones from the Mount Vernon clays, both at the original locality discovered 

 by mo on Octol)ei' 10, 1892, and also in White House Bluff, at a locality 

 discovered on December 5, 1892. 



Nearly the whole month of July was devoted to a critical reexamina- 

 tion by Professor Fontaine and myself of the Potomac beds of the District 

 of Cohunbia, Maryland, and Virginia from Baltimore to Fredericksburg. 

 We confirmed my previous observation that the conditions to the north- 

 west and north of Washington closely approaches those of Virginia, the 

 principal difference being that the Rappahannock sands are not lithihed 

 and are somewhat less feldspathic, Ijoing generally white and cross-bedded. 

 But in passing eastward on the strike these sands are soon overlain by the 

 dull-red clays characteristic of the Maryland exposures. This condition 

 begins at Eckington, within the city, and is well shown in numerous 

 cuttings on tho Metropolitan jjranch of the Baltimore and Ohio Railroad, 

 notably at Terra Cotta. Typical basal clays may be seen at Lamond, 

 also on the railroad. The plant bed at the l:)ottom of the new reser\-oii- 

 was foimd to be in lignitiferous clays of the same age underlying the 

 sands, which liere hold large quantities of silicified wood. At many 

 points northeast of Washington the dull-i-od clays that overlie the white 

 (here often yellowish and ferruginous) sands are in turn o\erlain 1)\- a 



