MARYLAND GEULOCilCAL SLKVEY 139 



It will 1)L' si'cii froiii the table above that the Eocene ha? no soil 

 equivalent, because buried too deeply under more recent materiah Even 

 the Miocene, with its three formations, plays but small part in the soils 

 of the present time. Almost the entire land surface is derived from 

 the three foi-niations of the Columbia Group of the Pleistocene period. 

 These three divisions are the Sunderland, the Wicomico, and the Talbot — 

 named in the oi-dor of their deposition. 



The oldest formation, the Sunderland, exists as an almost continuous 

 sheet of gravel, clay, and loam, covering the highest upland portions 

 of the county. According as the component materials differ in texture 

 and structure, depending upon the origin of the material and upon 

 the methods and conditions of its deposition, it gives rise to the Norfolk 

 loam, the Leonardtown loam, the Susquehanna gravel, the Windsor 

 sand, and the Xorfolk sand. The last two of these soils occur also 

 as derivatives from the Choptank formation of the Chesapeake Group. 



The Wicomico, which occurs as a fairly well-defined terrace along 

 the Patuxent and its tributaries, gives rise to the Sassasfras loam over 

 the main terraces and occasionally to small areas of Norfolk sand, where 

 these terraces are continued inland along the larger streams. 



The latest formed Talbot terrace presents two characteristic soil 

 types — the meadow areas of the for(>land and the Sassafras sandy loam. 



It will be noticed that several of the geological formations give rise 

 to two or more soil types, and that some of the soil types are derived 

 from two or more geological formations. This emphasizes the fact 

 already noted that the geological classification of sedimentary rocks is 

 based upon the time when the material was deposited; that is, upon 

 the relative age as shown by the stage of developniont of life' forms 

 rathei- than upon the character of the materials. The soil classification, 

 on the other liand. is based upon the character of the material without 

 regard to its age. 



Tlu'i'c ai-(> several interesting problems regarding the orign'n and 

 deposition of the Pleistocene deposits. The beginning of the Pleistocene 

 stage of deposition was marked in Calvert County by the contribution 

 of rather coarse sand and gravel, containing some boulders of such 



