56 TRANSACTIONS OF THE [1889 



the right hand, and where the fossil shells in countless numbers 

 project from the marl as far as the sight can reach. In these 

 deep gashes, cut in the side of a highland which rises more 

 than a hundred feet above the river terrace, we have striking 

 examples of the course selected by the streams in working their 

 way out to the river or creek. Besides, showing how torrents 

 of rain cut back into the adjoining bold hills, make lateral 

 gullies, and establish a complex system of drainage which is 

 ever modifying the arrangement of the contours of surface. 



From the vicinity of the river we pass over the almost flat 

 slope of the Quaternary river-terrace, until a point is reached 

 along the bed of a brook, the stream of which is usually not 

 more than five or six feet in width, where the hills begin to 

 rise with a gentle grade. At this part of the mouth of the 

 stream, a marshy spot usually spreads widely around into the 

 underl}dng clay. Entering between the low ends of the hills, 

 we find that the stream has opened a flood-channel, perhaps 

 fifty feet or more in width. Keeping farther in, the hill 

 quickly rises, but is covered on either side by the sandy loam 

 washed from the upper levels. Proceeding farther into the 

 ravine, the high hills soon begin to tower on both sides ; but 

 only at intervals do we meet with a precipitous exposure of the 

 beds. The most abrupt cutting of the walls has been on that 

 side which inclines towards either the south or the east ; but 

 on this side of the ridge, the steep bank is on the more southerly 

 border of the stream. On this side the Eocene compact black 

 marl forms the base of the exposures, and these are separated by 

 a wide interval of mixed greensand and loam. These black 

 marls are in part almost as dense and plastic as those of the 

 Cretaceous, and are far more closely packed with several species 

 of fossil shells. The bed first reached in a ravine running 

 out from a point nearly northeast, next the boundary between 

 Prince George's and Charles counties, shows an abrupt cliif, 

 rising at that point about thirty feet above the bed of the 

 stream, but connected with a higher hill farther back. Here 

 Crassatella capricranium is densely packed in the lower portion, 

 followed next above by Dosiniopsis meehii, an occasional speci- 

 men of small Ostrea compressirostra, and a few Turritella 



