1888] MARYLAND ACADEMY OF SCIENCES. 25 



ferruginous sandstone occur at higher levels, and may be seen 

 in the strata along the banks extending up South river. 



Leaving this region and passing over into Prince George's 

 County, we reach the classic ground of American paleontolo- 

 gists, in the vicinity of Upper Marlboro. Here fossil shells 

 abound. High cliffs bound the western branch of the Patuxent 

 river as it passes along the north side of the town, leaving a 

 gorge for the stream, which is reduced to the size of a narrow 

 creek, and flows out into a low plain that has been caused by 

 erosion of the adjacent country. The cliffs are abruptly steep 

 on the southwest side, and display large broken masses of 

 siliceous shellroek, at an elevation of about fifteen to twenty 

 feet above the water. On the northeast side of the creek the 

 cliffs rise more than fifty feet above the bed of the stream, but 

 are set back from it, and are less abrupt, because of the erosion 

 which has cut away the upper portion for a few rods and has 

 left a sloping terrace next the base. These cliffs are composed 

 of greensaud marl, which is unevenly stained with iron precipi- 

 tate above the lower portion, and which becomes more sandy 

 and ferruginous toward the top, the upper sui»face being covered 

 by a ferruginous clay-loam. Along the lower terrace on the 

 northern side, and at an altitude of about ten feet above the creek, 

 the siliceous shell limestone is laid bare, and rests on, or projects 

 out of, the marl in broken masses, which belong to a stratum 

 originally five or six feet in thickness. These masses are of very 

 variable size, ranging from three to five feet in length and two 

 to three feet in thickness. Some of them have dropped to a low 

 level, and still others rest in the floodbed of the stream. 

 Proceeding down the creek, we find the low terrace studded 

 with masses and boulder-like pieces of this rock throughout a 

 distance of about half of a mile. Below this, the low flat region, 

 leading off towards the marshy ground in the direction of the 

 Patuxent river, gives no further indication of the stratum of 

 rock. Weather and subaerial agencies, such as frost and heat, 

 have been busily breaking up the larger uncovered layers of 

 this silicified shell marl, so that every year reduces it to smaller 

 size and dissolves out much of the shelly matter that is not well 

 indurated. In these masses the Eocene shells are compacted as 



Dec. 19, '88-JAN. 12, '89. 



