MARYLAND GEOLOGICAL SURVEY 83 



together in a confusing manner. No one of them is confined to any- 

 definite stratum, but may occur anywhere throughout the section. Irreg- 

 ular beds or lenses of loam, sand, or gravel are locally developed through- 

 out the formation. Taken as a whole, the gravel is considerably decayed 

 and rather fine grained, but in the vicinity of the Piedmont Plateau it be- 

 comes very coarse and is imbedded in a compact sand or stiff reddish clay- 

 loam. Southeast of Washington, at a moderate distance from the Pied- 

 mont border, the red or orange-colored gravel and clay gradually gives 

 place to a buff or mottled clay-loam in which only small quantities of 

 fine grained gravel are present. Usually the Lafayette is capped by a 

 deposit of loam varying from a few inches to 10 feet or more, and with an 

 average thickness of about 5 feet. At times it is highly argillaceous, 

 at other times decidedly arenaceous, but as a general rule, it is of very fine 

 texture. Along the Piedmont border this loam contains considerable 

 iron and has a decided orange color, but in southern Maryland changes 

 to a buff or yellow. In color and also in texture it in many places 

 suggests the loess of the upper Mississippi valley. On the broad 

 Lafayette plain the loam shows a very pronounced mottling of drab and 

 brick red. This is espcially noticeable when the material is wet. It is 

 seen in numerous road cuts, especially to the west of Brandywine. The 

 heterogeneous character of these materials furnishes evidence of the 

 varied source from which the gravels have been obtained. Quartz and 

 other crystalline pebbles indicates the Piedmont as the source from which 

 they were derived; sands and broken iron crusts give evidence of the 

 Potomac ; fossil-bearing pebbles prove their derivation to have been from 

 the Paleozoic formation to the westward; and finally, decayed blocks of 

 Newark sandstone are occasionally met with. In southern Maryland 

 much of the material has been derived from the Miocene beds. 



The Lafayette and subsequent formations changed the proportion of 

 their constituents so rapidly from place to place that sections could be 

 multiplied indefinitely, each one showing something a little different 

 from all the others. It is, therefore, considered unnecessary to give 

 more than one type section for each formation. 



