MARYLAND GEOLOGICAL SURVEY 145 



their edges overlapping like the shingles on a roof. Some of the clay 

 masses are very regularly lenticular, others are irregular; while in some 

 instances this structure is only partially indicated. Along the laps 

 of the clay lenses are to be found little seams of sand with occasionally 

 pockets or masses of sand of greater extent. Some fine gravel is 

 mixed with the sand. 



The entire structure suggests the accumulation of a large number 

 of clay masses which have become flattened through the pressure exerted 

 by overlying materials. These clay masses were probably derived by 

 wave action, rolled along a somewhat sandy shore Hue or sea bottom, 

 and finally deposited in more quiet water. 



The formation is almost uniformly underlain by sandy and gravelly 

 layers from which the sand content might have been derived; and 

 the amount of sand in a given mass decreases as the line between the 

 sand and clay strata is farther removed. 



This structure of the subsoil of the Leonardtown loam is one of its 

 marked characteristics, not only in Calvert County but over larger areas 

 of the same soil formation in adjoining regions. It indicates a marine 

 or estuarine origin and shows that the soil was deposited as a pebble 

 or boulder mass of clay in water of a moderate depth. The agricultural 

 significance of this peculiar structure is also marked. 



The soil of tlic Leonardtown loam areas consists of a yellow, silty 

 loam, containing scattered pebbles of small size. Its usual depth is 

 about one foot and it is underlain by a clay loam subsoil having the 

 characteristics already described. The total depth of soil and subsoil 

 varies greatly, both because of differences in thickness of the original 

 deposit and because erosion has not been uniform in different localities. 



The Leonardtown loam subsoil acts as a heavy clay in its relation- 

 ship to the circulation and retention of soil moisture, though a mechani- 

 cal analysis of any given portion of it would show it to be a somewhat 

 sandy loam. 



Water, in circulating through soils and subsoils, depends for its rate 

 of motion upon the size and arrangement of the spaces existing between 

 individual soil particles. Thus a coarse sandy soil has less actual open 



