26 THE PHYSICAL FEATURES OF PRINCE GEORGE S COUNTY 



GENERAL CONTRIBUTIONS. 



Maclure, in 1800, was the first geologist in this country to attempt 

 to separate the different kinds of rocks on the basis of lithologic 

 differences. These divisions were termed formations. He noted the 

 wide difference in the characters of the rocks composing the Piedmont 

 Plateau and the Coastal Plain and on the basis of these differences 

 established two formations. He called the crystalline rocks of the 

 Piedmont Plateau the "Primitive formation," and the unconsolidated 

 deposits of the Coastal Plain the "Alluvial formation." His con- 

 clusions, accompanied by a colored geologic map on which these 

 divisions were represented were published several times but most 

 fully in 1817. The work of Maclure served as a great incentive to 

 geologic research in this country outlining as it did the methods of 

 work which have been followed since his time and which have yielded 

 such important results. 



Ducatel, State Geologist of Maryland from 1834 to 1840, was the 

 first person to publish any definite information of value concerning 

 the geology of Prince George's County. In his first report, pub- 

 lished in 1834, he refers to the fossiliferous deposits at Upper Marl- 

 boro and Fort Washington and discusses the economic value of the 

 marls and iron ore of the county. He elaborates upon the same 

 subjects in his report for the year 1835, and in his 1836 report (pub- 

 lished 1837), he again calls attention to the shell and greensand marls 

 occurring within the region, which he thinks might prove valuable as 

 fertilizers. In the latter publication he discusses the physiography 

 and geology of Prince George's County in a more detailed manner 

 than had any of his predecessors. 



The reports of Alexander, the Topographical Engineer, issued in 

 connection with the reports of the State Geologist, contain many good 

 descriptions of the physical features of the county. In his "Report 

 on the 'New Map of Maryland, 1835" the characteristics of Pisca- 

 taway Creek are discussed and profile drawings of it are included in 

 the report. He described the manner in which the creek was being 

 filled by sediment brought in by tributary streams and discussed the 

 feasibility of constructing canals along either side of the creek to 

 receive the surface drainage and thus keep the stream navigable. 



