534 T. L. WATSON LITHOLOGICAL CHARACTERS OF VA. GRANITES 



or granite-gneiss. The two massive granites are designated above as the 

 light gray granite and the dark blue granite. Three periods of intru- 

 sions are accordingly represented in the following order, beginning with 

 the earliest: (1) The granite-gneiss, (2) the Eichmond-Petersburg light 

 gray granite, and (3) the Eichmond-Fredericksburg dark blue granite. 

 This succession is plainly indicated in the field and is further confirmed 

 by microscopic evidence. 



CONTACTS 



The numerous quarries worked in the vicinity of Eichmond afford 

 excellent opportunity for studying the contacts between the fresh granites 

 of the three types named above. As noted in the description detailed 

 above of the three types, the difference in color, texture, and structure 

 render them easy of differentiation. From the large number of contacts 

 examined not one has shown the presence of contact minerals. Several 



fray ) ^^B/ae \*A\ <?W/^ 



Figure 3.— Relations of the Blue to the Gray Granite. 

 As shown at the Netherwood quarry west of Richmond. Scale, V' = 159'. 



of the contacts show inclosures of the older granite in the newer one. 

 At one of the contacts between the light gray and the dark blue granites 

 in the Netherwood quarry the younger or dark blue granite contains 

 numerous irregular and varying size fragments of the light gray granite, 

 as shown in figure 2. Again, other exposures in the same quarry reveal 

 the true relations of the two granite types. As shown in figure 3, the 

 dark blue granite invades the gray granite in two separate, nearly vertical 

 dike-like arms. Figure 2, plate 69, is from a photograph of one of the 

 arms of the dark blue granite showing jointing of the rock. The same 

 relation of these two types is equally well shown in the dark blue granite 

 penetrating the light gray granite in the Philadelphia quarries at the 

 head of the settling basin near Eichmond. 



