APLITES AND PEGMATITES 



537 



to be: (1) Granite-gneiss, (2) Kichmond-Petersburg light gray granite, 

 and (3) the Kichmond-Fredericksburg dark blue granite. As shown in 

 the accompanying figures, sketched from quarry openings in the field, 

 the granite mass of each intrusion was accompanied by the formation of 

 pegmatitic material. Some of the pegmatites intersecting the dark blue 

 granite which represents the latest of the granite intrusions also pene- 

 trate the light granite, and in some cases the earliest of the intrusions, 

 granite-gneiss. These conditions are well illustrated in figures 1 and 5, 

 which show that the latest formed pegmatites intersecting the dark blue 

 granite also extend into and intersect respectively the granite-gneiss and 



v / \ V \ \ 



'C\'3/ue 'Gr4tirte\*'-} 





Figure 5.— Contact between Blue and Gray Granite. 



Netherwood quarry, west of Richmond. The same pegmatite cut- 

 ting both granites is shown. 



the light gray granite ; also figure 1 shows that a pegmatite which char- 

 acterized the earliest period of intrusion, granite-gneiss, is abruptly cut 

 off by the intrusion of the dark blue granite into the granite-gneiss. It 

 will be observed from the figure that where the pegmatite is cut off by 

 the dark blue granite it is equally as wide as in any other portion of the 

 dike, traced for some distance in the exposed granite-gneiss. Moreover, 

 those pegmatites which belong to the latest period of intrusion and which 

 intersect the dark blue granite are found intersecting each other in such 

 manner as to indicate earlier and later formation. Figure 6, which 

 shows this, also shows that the oldest or intersected pegmatite is faulted 



