TLANT LOCALITIES. 23 



White House wharf, and extends several hundred yards down tlie river. 

 The material composing it is almost wholly Potomac, of which it shows 

 fully eighty feet. This is capped Ijy about fifteen feet of Quaternary. The 

 lowest portion of the bluff, for fifteen to twenty feet, is a coarse sand, nearly 

 white in color, and consolidated to a pretty firm rock. Higher the sandv 

 matter is yellowish gray, or brownish yellow, from oxidation and from the 

 ailmixture of some colored clay, ('lav lavers, balls, and pockets occur on 

 both horizons. Abt)ut sixty feet above water level is a prett}' well defined 

 layer two to four feet thick of mixed sand and disturbed clay. This 

 seems to be almost pure clay in some places, and may be detected by the 

 water that issues from the fiice of the bluff. In a number of places it con- 

 tains a good many bits of plants, among which some undeterminable coni- 

 fers and small fragments of THoonites Buchianm may be seen. 



At only one place have well-preserved impressions been found, about 

 seventy-five yards below the old wharf Here a large amount of talus 

 forms a steep slope up to the foot of a perpendicular bank about twenty 

 feet high. In the base of this bank the bed above described occiu-s The 

 material is difficult of access and collecting is dangerous, since the bank 

 al)ove threatens to come down upon one working at its base. The clay 

 presents the usual structural features of the disturbed clays ; but its min- 

 eral character is unusual, and not found in many of the exposures of the 

 layer in the blufT. It has a light buff color, and is very fine in texture and 

 plastic; the lumps and masses are so mixed with sand in redeposition and 

 so much contorted that it is not eas>' to obtain good s^jecimens. The im- 

 pressions of leaves are numerous, but the species of plants are few. The 

 dicotyledon Sapindo2)sis variabilis, with pinnate leaves, so common at the 

 two localities near Brooke, gives nearly all the imprints. The state of 

 preservation of these leaves is similar to that of those seen near Brooke, 

 the parts of the leaf most conmionly found there being most numerous 

 here also. This locality will be referred to as "White House Bluff." 



Fragments of plants with some determinable parts occur at Mount 

 Vernon, on the Potomac River, two miles above White House, and also at 

 Fort Washington, on the Maryland shore, about three miles east of Mount 



