311 



the latter case the patches are generally richer in the more basic consti- 

 tuents, such as plagioclase and biotite they may be described in many 

 cases as patches of diorite in granite. Thus, these inclusions bear the 

 same relation to granite that the nodules of peridotite, so common in 

 many Continental basalts, do to the rock in which they occur. It seems 

 impossible to avoid the conclusion that somehow or other these patches 

 are the result of differentiation accompanying the crystallization of the 

 original magma. As this point is one of general interest we will quote 

 Mr. PHILLIPS' analyses of the granites and the more basic inclusions which 

 occur in them before proceeding to describe the rocks of special localities. 



I. la. II. Ha. 



Si0 2 ... 69-64 ... 65-01 ... 73'70 ... 64-39 



A1 2 3 ... 17-35 17-37 ... 14-44 ... 15-99 



Fe 2 3 ... 1-04 ... 4-95 ... '43 ... 1-47 



FeO ... 1-97 ... 1-86 ... 1'49 ... 5'98 



MnO ... tr. ... tr. ... tr. ... tr. 



CaO ... 1-40 ... 211 ... 1-08 ... 2'57 



MgO ... -21 ... 1-34 ... tr. ... 1'67 



K 2 ... 4-08 ... 1-82 ... 4-43 ... 2-46 



Li L ,0 ... tr. ... tr. 



Na.0 ... 3-51 ... 4-14 ... 4'21 ... 4'96 



PA tr. ... tr. ... tr. ... tr. 



HX> -72 1-43 -61 -95 



99-92 100-03 ... 100-39 ... 100-44 



Sp. Gr. 2-72 2-73 2-69 2'73 



I. Grey granite from Gready in the parish of Luxulyan, Cornwall. This granite 

 contains two micas and an occasional crystal of tourmaline. Garnet is sometimes present. 



la. Dark ovoid patch in the above, containing more biotite and plagioclase than the main 

 mass of the rock. 



II. Pink granite of Peterhead, near Aberdeen. Composed of quartz, orthoolase, plagio- 

 clase and black mica with a little apatite and titanite. 



Ila. Dark coloured and fine-grained patch in the above. Contains more plagioclase and 

 dark mica than the main mass of the rock. 



It will be seen from the above analyses that the basic patches 

 are poorer in silica, richer in lime, iron and magnesia, and poorer in 

 alkalies than the rocks in which they occur. Moreover the relations 

 of the alkalies are different in the rocks and in the inclusions ; in 

 the former potash predominates, in the latter soda. As intimately 

 connected with the phenomena of inclusions we may mention the fact 

 that in certain localities granitic and dioritic rocks vein each other 

 in the most intricate manner ; not as if the one rock had been 

 intruded into the other but rather as if the two rocks were the result 

 of differentiation in a magma during solidification. If we suppose move- 

 ment to take place in a magma after the differentiation of dioritic masses 

 and when the mother liquor possesses the composition of granite we 

 can readily understand how dark patches and streaks of dioritic rock 

 may occur in granite. According to this view the want of homogeneity 



