THE LAFAYETTE FORMATION. 177 



Sand forms a rather unimportant part of the Lafayette deposit. Such as 

 is present was doubtless mainly derived from the Potomac beds. Lenses of 

 sand are frequently found in the gravel deposits, but rarely does the sand 

 form beds of any considerable thickness or areal extent. It usually serves 

 as the matrix for the gravels, or else is intimately mixed with the loam. 



At points where the formation has suffered little erosion the uppermost 

 beds consist of loam, varying in thickness from a few inches to 10 feet or 

 more. Observations made in many places seem to indicate that this loam 

 is much thicker in the vicinity of Eichmond than elsewhere in the State, 

 and there consists of a reddish-brown clayey loam which has been utilized 

 in the manufacture of brick at several points near the cit3^ When wet the 

 loam not infrequently shows a very pronounced mxottling of drab and brick- 

 red. Although the loam cap is relatively free from bands of gravels, they are 

 not entirely absent. Single pebbles are not uncommon in the loam, and at 

 times there are well-defined beds of gravel and sand. Some of these pebbles 

 are well rounded but angular quartz fragments are also present, particularly 

 in proximity to the crystalline rocks. There the Lafayette deposits may 

 bear such a striking resemblance to the residual materials of the metanior- 

 phic rocks that the presence of occasional rounded water-worn pebbles mixed 

 with the angular fragments is the only clue to the real character of the beds. 

 In such cases the bulk of the material does undoubtedly consist of such 

 residuum which has only been transported a short distance, although, in this 

 process, water-worn gravels which have been transported greater distances 

 have become mixed in small amounts with the residual clay. At the brick 

 yard near the reservoir west of Eichmond there is such a clay deposit about 

 18 feet in thickness, the upper part of which is deep red in color, the lower 

 mottled and white, which could scarcely be distinguished from the residual 

 material, were it not for the presence of a few rounded pebbles distributed 

 through the deposit. 



The variable character of the Lafayette materials renders detailed sec- 

 tions of little value, but the following section exposed in northwest Eich- 

 mond along the Seaboard Air Line Eailroad, near Beacon's Quarter Branch, 

 furnishes a good idea of the materials. 



Section exposed in Northwest Richniond near Beacon s Qiuirter Branch. 



Feet 

 Red clay loam containing many small rounded pebbles irregularly distributed 



throughout the bed 9 



Poorly sorted coarse and fine gravel in matrix of coarse sand, red clay, or 



arkose ( exposed ) 18 



Total ■ 27 



12 



