MARYLAND GEOLOGICAL SURVEY 29 



defined it as " all deposits derived from causes now in operation," such 

 as accumulations of mud along river courses, drifting sand, peat-bogs, etc. 

 A few years later, in 1839, he came to the conclusion that the huge 

 angular blocks in the " Diluvial " were transported and deposited there 

 by glaciers or icebergs. 



While Conrad was still engaged in studying the Coastal Plain forma- 

 tions, Ducatel and Alexander began the publication of a series of State 

 reports which covered the period between 1834 and 1839. Alexander was 

 engaged in the engineering phases of the work, while Ducatel devoted his 

 time to geological investigations. As his attention was directed more to 

 the economic side of geology, he gave his efforts to the iron ore-bearing 

 clays of the Potomac beds and the shell and marl deposits of the Tertiary 

 formations, and paid little attention to the overlying surficial deposits of 

 loam, sand, and gravel. He, therefore, added very little to the knowledge 

 which was current at that time, but regarded the entire mantle as 

 " diluvial,'-' in this respect following strictly in the footsteps of his 

 predecessors. 



Five years later H. D. Rogers, in an address delivered at the meeting 

 of the Association of American Geologists and Naturalists, referred 

 briefly to the fossiliferous deposits at Cornfield Harbor (Wailes Bluff). 

 He believed them to be either post-Pliocene or Pleistocene and drew 

 attention to the fact that they contained certain forms which at the 

 present day inhabit warmer waters. He suggested that this change 

 of climate might be clue to a change in the course of the Gulf Stream 

 or to an incursion of a current of icy water from the north or to " some 

 more inscrutable agency." 



After this discussion of Rogers, nothing more seems to have been 

 contributed on the question until Desor, eight years later, referred once 

 more to the deposits at Wailes Bluff. He gave a list of the fossils 

 from this locality as determined by Conrad and concluded with Rogers 

 that the beds were of post-Pliocene age and correlated them with the 

 Laurentian quaternary of the north. In regard to the boulders found 

 scattered over the surface, he believed them to have been floated down 

 the Potomac on icebergs. When Tyson referred to the surficial deposits 



