1889] 



MAEYLAND ACADEMY OF SCIENCES. 59 



incumbent loam or sand. These elongated beds of fossils are 

 not often continuous for very long distances in this region, and 

 they do not always follow in the vertical order given above. 

 Denudation or erosion has sometimes carried away one or more 

 subdivisions of the series, and at other points it would seem 

 that one or another of these large colonies of shells had failed to 

 be present. 



Returning to the great Eocene deposit on the Beard property, 

 up the Piscataway Creek, about one mile from the Fort Wash- 

 ington wharf, we find a most remarkable example of the type of 

 structure and composition of the formation, as it exists in the 

 western part of Prince George's county. Here is observed a 

 great deposit of marly sand and varied material, full of broken 

 fossils mixed with the comminuted carbonate of lime derived 

 from the vast numbers of shells which crowded the locality. 

 This material is hard, but far less coherent than the correspond- 

 ing bed in the vicinity of Upper Marlboro, and it readily shat- 

 ters into irregular slabs and laminar chalky fragments by being 

 struck with the hammer. The pieces as they are broken open 

 disclose specimens of the Crassatellas with fragments of a chalky 

 shell adhering, most of which drops off when they are removed 

 from the matrix. Such is also the case with Dosiniopsis and 

 Turritella; but individuals of Glycimeris elongata can be extracted 

 with the shell almost entire, as may also be done occasionally with 

 the shells of Ostrea and small specimens of Turritella mortoni. 

 Cardita planicosta, of small size, also occurs in this bed, but it is 

 never obtained with unbroken shell, and it is usually present as 

 an indurated cast. This more or less indurated member of the 

 section shows that the shells have been thrown together in 

 heaps, in a most disorderly manner. The material has evidently 

 been pushed into a widely eroded space between two high bodies 

 of Cretaceous Black Lower Marl and fills up all the interval ; 

 while farther back it has risen to a higher level and spread 

 westwardly, in a thin layer, over the top of the more loamy 

 greensand marl which rests upon the Cretaceous Lower Black 

 Marl. 



The lower ten feet of this deposit is closely packed with 

 friable shells of Crassatella protexta, another species, possibly C. 



