1888] MARYLAND ACADEMY OF SCIENCES. 31 



The foregoing observations are the results of studies conducted 

 at remote intervals during the past twenty years, at first in 

 conjunction with Mr. Philip T. Tyson, with the view to settle 

 with greater precision the boundaries, detailed composition, 

 thickness, and origin of the sedimentary formations of the 

 State of Maryland. Even at this late date, after so much labo- 

 rious work has been done in examining the hills, river beds, 

 and ravines, many pressing minor questions yet remain to be 

 settled. The position and principal relations of each great group 

 seem now to be about settled, and the work of the future will 

 have reference to the more minute details, and to filling out the 

 list of fossils. 



One problem of great interest, however, deserves some notice 

 before closing this subject, and that is, the relation of the 

 mixed greenish and ferruginous marl sands to the fine gray 

 slightly argillaceous sand as seen between Aisquith's Creek and 

 the Mill-pond above Chase's Creek. The upper portion of 

 these ferruginous marl sands holds specimens of Ostrca com- 

 pressirostra and casts of Dosiniopsis 3Ieehii. If, therefore, we 

 include the whole body of this great member, which stretches 

 all the way from the mouth of the Severn to the Mill-pond and 

 then rises into the hills, we shall have to restrict the Cretaceous 

 of the Western Shore to a width of country not much exceed- 

 ing three miles. 



The black deposits of the Lower Marl beds, in this region, 

 extend from near Cedar Point to Aisquith's Creelv, and next 

 above them in the river bluffs ascend the lower argillaceous 

 green sands, above which are seen the fine gray slightly argil- 

 laceous sands, overlaid by the ferruginous marl sands, and 

 these latter continue up to the well distinguished Eocene sands 

 and sandstones near the surface. The fine gray slightly argil- 

 laceous sands seem to mark a deposit between the two forma- 

 tions ; and, being composed of such loose materials, it would 

 readily have blended with the soft marl laid down over it, and 

 thus the line of contact might have been left undefined. Much 

 investigation is still needed to settle the exact thickness of 

 these two groups of strata, and to determine precisely the 

 conditions which prevailed in Maryland at the close of the 

 Cretaceous period. 



