1889] 



MARYLAND ACADEMY OF SCIENCES. 49 



feet above the level of the creek. No recognisable fossils were 

 taken from this upper division, although indications of their 

 presence were observed at occasional intervals. This greenish 

 marl extends upwards into a more ferruginous sand, which is 

 only the iron-stained and water-washed portions of its own 

 body, from which the clay has been removed and the iron stained 

 into the grains of sand. This upper part also joins a coarser 

 sand of a more decided red color, of variable thickness, which 

 extends upwards into the more gravelly sand of the Quaternary 

 superficial stratum. On top of this last, boulders of Potsdam 

 sandstone, quartz, diorite, and many other kinds of rock rest, 

 often in a thick deposit of gravel and coarse pebbles. This 

 material, varied with wide intervals of more or less gravelly 

 yellowish loam, spreads back from this section, and forms a 

 large part of the surface for a distance of several miles. 



In that part of the section which lies nearest to the Potomac 

 river, the lower parts are much obscured by fallen debris and 

 clay from its higher portions, and by the dense growth of 

 bushes, vines and trees which covers all but the steepest slopes. 

 However, by clearing oif the surface and digging through the 

 thinner parts of the fallen material, we reach precisely the same 

 beds as those enumerated before. 



Directly beneath the fort we perceive a body of material which 

 does not again appear until we have proceeded at least half a 

 mile farther up the Piscataway. That is the presence of Eocene 

 oyster and other broken shells spread over the steep incline for 

 fifty feet or more, at an elevation of thirty to forty feet above 

 the water. Upon close examination, however, the fossil shells 

 are found to be a part of the Eocene mixture which was thrown 

 down the hill, most likely at the time when the excavation for 

 the fort was made. No Eocene appears in place directly in the 

 composition of this hill, although scattered fossils have been 

 picked up at various times on the surface of the gullies adjoining 

 the fort. 



The second bare exposure of the Cretaceous in the continua- 

 tion of this hill appears at a distance of about three-quarters of 

 a mile behind the fort. This is a much longer bold cliff than 

 the former, and is cut back into a cove, which gives an extensive 



NOV. '20, '89. 



