416 JV. II. Darton — Magothy Formation of Maryland. 



thin capping of weathered Severn beds. The coarseness of 

 the upper part of the Magothy is not so pronounced in this 

 exposure and the sands for some distance below are of the usual 

 moderately coarse, loosely bedded type. JSTear their base, thin, 

 interbedded carbonaceous layers gradually come in and finally 

 form an irregular lignitic layer with white sand streaks. Below 

 this are irregular layers of brown sandstone two or three feet 

 thick exposed along the beach. 



In the next bluff up the river, Potomac, Magothy and Severn 

 beds are exposed in a section thirty feet in height. The 

 Severn caps the bluff to a thickness of from six to nine feet 

 and consists of fine, argillaceous sands weathered to a gray- 

 buff color. They lie on a very even but clearly defined ero- 

 sion plane exposed for nearly a hundred feet along the bluff. 

 The Magothy beds average twenty feet in thickness but are 

 several feet thicker at several points. They consist of regu- 

 larly bedded, loosely compacted, gray sands with light buff 

 streaks and blotchings containing thin streaks of brown sand- 

 stone above, and large masses of brown sandstone below. They 

 lie on a very uneven surface of the densely packed sands and 

 clays which as before stated characterizes the upper part of 

 the Potomac formation in this region. One of the most nota- 

 ble irregularities of this surface is an old channel four or five 

 feet in depth in which the Magothy beds come down nearly 

 to water level. The Potomac deposits lying next below the 

 Magothy formation are very densely packed, gray sands, in part 

 lithified. They also contain a short streak of carbonaceous 

 materials. Below, they give place abruptly to a series of lenses 

 of very tough pearl-gray sulphurous clay with sulphur crusts 

 on its surface. Underlying this clay are several masses of 

 sandstone which outcrop at the base of the bluff. A person 

 unfamiliar with the complicated stratigraphic relations in the 

 coastal plain formation would be puzzled by this exposure with 

 its several exceptional features in the Potomac formation, and 

 their apparent unconformities, and by the two horizons of 

 brown sandstones. 



Ascending the river the dip brings up in succession lower and 

 lower beds which exhibit very plainly the true general relations. 

 There are several bluffs on the north shore exposing the very 

 compact sands and clays of the Potomac, unconformably over- 

 lain by the loosely bedded coarse, white Magothy sands here con- 

 stituting the surface formation. In a bluff about a mile and a 

 half above Pound Bay the Potomac beds attain an elevation 

 of twenty-two feet and are overlain by from eight to ten feet 

 of Magothy sands. This exposure is the key to the horizon of 

 the compact sands and gray sulphurous clays for they are finely 

 exhibited, grading laterally and downward into looser white 



