92 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND 



products left in the soil by the weathering of the limestone. The top, 

 middle and lower portions are especially well characterized by siliceous 

 products, such as chert, flint and sandy shale fragments, which are dis- 

 cussed in detail in succeeding paragraphs. 



LITHOLOGIC CHARACTER. Although the Beekmantown limestone 

 differs considerably in its lithological development in the eastern and 

 western parts of the valley, the formation as a whole is composed of 

 much purer limestones than the underlying Conococheague. On the other 

 hand its purest beds are inferior in calcium carbonate content to the high 

 average of the overlying Stones Kiver limestone. The purer limestones 

 of the Beekmantown are interbedded with greater thickness of relatively 

 impure finely laminated beds which occur, or at least outcrops, so fre- 

 quently that the presence of these laminated limestones is a good criterion 

 for the formation. This characteristic minute lamination of the average 

 rock of the formation is due to impurities in the rock and most apparent 

 on weathered surfaces. Pink and white fine grained marbles in ledges of 

 considerable thickness also are of common occurrence in the Beekman- 

 town, especially in the lower half of the formation. Marbles occur in the 

 underlying Conococheague limestone, but as they are always associated 

 with the characteristic siliceous banded limestone of that formation they 

 are readily distinguished from the marble beds of the Beekmantown. But 

 it should not be forgotten that siliceous banded limestones quite similar 

 to those of the underlying Conococheague beds occur also in the lower 

 fifth of the Beekmantown. These are so constantly developed in tho 

 eastern half of the valley that the part containing them has been mapped 

 as a distinct basal division under the name of the Stonehenge limestone 

 member. This basal member can be recognized locally also in the western 

 part of the valley, but here its lithologic characters are hardly distinct 

 enough to warrant its separation in the mapping. 



As practically all of the Beekmantown areas of Maryland are covered 

 by gently rolling cultivated farm lands it is almost impossible to make 

 out the complete section of the formation in any particular place. How- 

 ever, by assembling incomplete sections in various parts of the valley the 



