22 TRANSACTIONS OF THE [1888 



On the Calvert county side of the Patuxent river, about 

 three-quarters of a mile below Lyons Creek, a section in the 

 abrupt bank rises about forty-four feet above the water and 

 exposes the following strata : at the bottom and up to eight feet 

 above water-level is a rather pure dark greensand marl in 

 which no fossils are observed ; next above this ascends twenty 

 feet of more siliceous greenish marl, in which are found casts 

 and shells of Turritella mortoni, Cardita planicosta, Ostrea com- 

 pressirostra, and Peduneulus stamineus ; above this occurs an 

 indurated siliceous rock, in broken masses, three feet thick, 

 enclosing shells and casts of the above named fossils, accompa- 

 nied by one or more species of Orassatella and the Cytherea 

 ovata ; and over this rest three feet of the Tripoli, upon which, 

 up to the surface, is a bed, ten feet thick, of sand mixed and 

 covered with fine quartz gravel. 



Farther down the river, above Hall's Creek, is another good 

 section, a few feet higher than the preceding, but in which the 

 lower bed of dark marl rises seven feet above the level of the 

 water, likewise exposing no shells, as in the corresponding bed 

 farther up the river, but this time supporting a much thicker 

 bed of Tripoli (about ten feet thick), capped as before by ten 

 feet of siliceous sand, with the gravel mixed and on the surface- 

 It will be noticed that in this exposure the stratum of indurated 

 shellrock fails to appear at the surface, if it is in fact really 

 present. Below Hall's Creek, for a distance of at least one 

 mile, the lower greensand marl stratum is seen to grow gradu- 

 ally lower, and below this point is no longer to be seen. The 

 upper part of the next upper and more sandy stratum, although 

 less conspicuous and more like common surface soil, is apparent 

 still lower down the river wherever the banks rise a few feet 

 above the water. The next great hill cut by the river is at 

 Holland's Clifis, two miles and a half below Lower Marlboro, 

 and there this mixed greensand forms a bed rising fifteen 

 feet above the level of the water, and is overlaid by the 

 usual Tripoli stratum, which is now thirty feet thick. It 

 deserves to be noticed at this place that above the immense 

 deposit of diatomaceous earth, up to within one or two feet 

 from the top of the hill, there is a bed of slightly ferruginous 



