140 THE SOILS OF CALVERT COUNTY 



large size that flowing water alone could not carry tliem. They could 

 have been brought to their present location only as debris frozen into 

 or borne upon the surface of floating ice. Some of these boulders 

 are very interesting, as they show the sources of the material, and 

 consequently give some idea of the land area existing at the time of 

 their deposition. Along Hunting Creek a boulder was found which 

 came from the granite area near Ellicott City. It possessed the same 

 peculiar texture as that granite — the large pink feldspar crystals sur- 

 rounded by smaller-sized crystals of other component minerals. There 

 are also found boulders of other rocks, notably gabbro diorite, a dark 

 green or black rock derived from the same general region. The pres- 

 ence of these boulders not only gives some idea of the land surface 

 existing in this former geologic period, but their transportation by 

 ice also gives some idea of the climatic conditions then existing. The 

 layer of material bearing these boulders, when now exposed, gives rise 

 to the Susquehanna gravel. 



After the deposition of this gravelly layer, clay and silt were brought 

 in. The peculiar structure of the subsoil of the Leouardtown loam 

 is due to the form this deposition took in its earlier stages. Clay 

 pebbles and clay boulders, probably derived from a shore line by wave 

 action, were rolled together as the first deposit over the gravel and 

 interbedded with sand and some small gravel. When these were firmly 

 packed down by the weight of accumulating sediments the clay pebbles 

 were flattened out into lense-shaped nodules, and the resulting soil 

 structure produces the effect of a heavy clay subsoil with sandy partings. 

 This feature and its results are described under the Leonardtown loam 

 soil type. 



The Leonardtown loam deposit was succeeded by silty and sandy 

 materials, giving rise to the jSTorfollc loam. After this the entire area 

 was slowly elevated above water level and stream drainage was estab- 

 lished over the newly formed surface. In many cases these streams 

 closely followed the stream beds occupied during Miocene times, as 

 these were only partly filled in during the Pleistocene submersion. As 

 erosion began again the newly deposited materials were removed, to- 



