CONTACTS, APOPHYSES AND INCLUSIONS 535 



At the McGowan quarry, several miles south of Richmond, and the 

 Cartright and Davis quarries, 3 miles north of Fredericksburg, contacts 

 between the granite-gneiss and the dark blue granite are beautifully 

 shown. At both places the granite cuts directly across the schistosity of 

 the gneiss, as shown in figure 1. Plate 72, figure 2, is from a photograph 

 of an inclusion of the gneiss in the blue granite. It is entirely clear that 

 the period of intrusion of dark blue granite was subsequent to the period 

 of deformation producing the schistose structure of the granite-gneiss. 



APOPHYSES 



At the Cartright and Davis quarries, 3 miles north of Fredericksburg, . 

 the sloping floor of the granite-gneiss in one of the openings contains 

 numerous large and small dikes or tongues of the dark blue granite pene- 

 trating the gneiss. These have the same texture, color, and composition 

 as the parent mass and they conform in part with the schistosity of the 

 inclosing gneiss and in part cut directly across it. Similar conditions 

 obtain at the McGowan quarry, several miles south of Richmond. The 

 Fredericksburg quarries furnish the best illustration of granite tongues 

 penetrating from the parent mass into the inclosing rock. 



INCL USIONS 



The inclusions are of two kinds: First, those which correspond in 

 composition and otherwise with the inclosing rock and plainly represent 

 fragments of the country rock torn off during the intrusion of the granite 

 containing them. In the Richmond-Fredericksburg areas the dark blue 

 granite in some of the quarries contains inclusions of the massive light 

 gray granite (figure 2) and of the gneiss (plate 72, figure 2). The 

 foliation of the gneiss is entirely preserved in the inclusions of the rock. 

 No appreciable metamorphism was observable in the contacts of the 

 county rock and the inclusions. 



The second type of inclusion is a massive basic segregation from the 

 magma. It consists of dominant biotite, a little feldspar and quartz, and 

 of variable sizes and shapes. Where observed, a tendency toward an 

 elliptical or much elongated mass is shown. The composition of these 

 bodies entirely comports with that of the inclosing rock, granite, except 

 that biotite is very largely in excess. These basic inclusions are abund- 

 antly developed in the hornblende-biotite granite of the Falls Church area, 

 where they assume very large dimensions in many cases. The Richmond, 



