1889] 



MARYLAND ACADEMY OF SCIENCES. 63 



rain-troughs connect with the upper half of this ravine, and 

 form a secondary and even ternary system of branches, in all of 

 which the marl is exposed at a distance of five to ten feet below 

 the surface of the country. No part of the mixed and broken 

 marl-rock can be found on this side of the promontory, nor do 

 we anywhere meet with the highly silicified shells which occur 

 so abundantly in places along the tributaries of the Piscataway. 



Directing our attention now to the region extending from 

 Upper Marlboro to the village of Queen Anne and from thence 

 up the Patuxent river to the vicinity of Governor's Bridge, we 

 meet with the Eocene beds and strata connected with somewhat 

 different physical conditions. 



The thick bodies of plastic black marl holding friable fossil 

 shells have disappeared, and in their stead we find beds and strata 

 of greensand marl, generally more or less loamy in composition. 

 The base of the hills near or below the level of the roads leading 

 northeast is generally found to consist of this kind of greensand 

 marl, and this directly overlies the stratum of silicious rock in 

 which the fossil shells are densely packed. All the deep wells 

 of the region have either penetrated to or through this rock- 

 stratum, and in some places it has proved too hard and thick 

 for the well-sinker to dig through. This fossiliferous stratum 

 keeps on under the hills all the way up to the vicinity of Gov- 

 ernor's Bridge, near which it becomes lost in the denuded up- 

 lands, and has not been seen beyond. It is also conspicuous in 

 the bed of the Patuxent river, next the village of Queen Anne, 

 and it is likewise found in the beds of the brooks at various 

 points in that vicinity. Throughout all this section of country 

 it is highly silicified, and holds the shells so firmly that it 

 becomes very difficult to extract them entire. 



The greensand marl which forms hills 30 to 50 feet high 

 above the river near this village, are more largely composed of 

 loose silicious sand than those a mile farther west, and the marl 

 agrees in composition with that which forms the cliffs along the 

 shore of Chesapeake bay, extending from the boundary of Bay 

 Ridge to Thomas Point. The island, however, on which the 

 old lighthouse here stands, forms an exception to the rest of 

 the marl on this coast, since it is stained black with car- 



