TEAGMENTS OP OTHER EOCKS CONTIINED IN GRINITE. 21 



on referring to the analyses p. 17, that the chief chemical changes 

 which have taken place in the rock are an increase in the proportions 

 of silica, iron oxides, magnesia, and potash, while there is a decrease 

 in the quantity of lime. 



Inclusions distinctly belonging to the two different classes not only 

 occur in the same granites, but good examples of both descriptions 

 may be sometimes found in the same cubic foot of rock. 



When schistose inclusions are found in ordinary eruptive granites, 

 they can only be regarded as fragments of extraneous rock which 

 have been caught up by the granite and enclosed within its mass. 

 In the case of granites which may, on the contrary, be supposed to 

 be of metamorphic origin, they will doubtless be looked upon by 

 those entertaining that opinion as portions of older rocks which 

 have, to a great extent, withstood the action of granitic metamor- 

 phism. 



The foregoing conclusions have been arrived at after an examina- 

 tion of only a limited number of rocks, but are probably capable of 

 more extensive application. 



EXPLANATION OF PLATE I. 



Fig. 1. Ovoid inclusion from Gready quarry, Luxulyan, Cornwall, one half 

 natural size. A fine-grained granite containing a large proportion of 

 dark mica : p. 7- 



2. Inclusion in granite from Foggen Tor, Dartmoor, natural size, por- 



phyritically enclosing granular quartz and a large crystal of orthoclase, 

 of which the angles are rounded : p. 8. 



3. Ovoid granitic inclusion in granite from Shap, Westmoreland, enclosing 



a rounded crystal of red orthoclase, four tenths natural size : p. 9. 



4. Inclusion in Shap granite, natural size, divided by a crystal of red 



orthoclase : p. 10. 



5. A similar inclusion, natural size, in the same block of granite, passing 



in a broken line through a crystal of orthoclase : p. 10. 



6. Segregationary inclusion of mica, one half natural size, Kemnay quarry, 



near Kintore : p. 12. 



7. Schistose inclusion in red granite from Peterhead, Scotland, two thirds 



natural size, composed of dark mica, granular quartz, and a few 

 crystals of felspar : p. 14. 



8. Inclusion, one half natural size, in granite from Groragh Wood, 



Ireland. In the centre of each of the light-coloured porphyritio 

 patches there is a crystal of sphene : p. 18, 



Discussion-. 



The Peesident said that he had examined cases of this kind in 

 the Aberdeen granite, and had found that some were really frag- 

 ments of another rock, and others concretionary. He therefore quite 

 agreed in the limited observations with which Mr. Phillips had 

 concluded from a much larger number. He thought the paper most 

 valuable, especially as bearing on the temperature at which granite 

 was formed. 



Mr. Attwood remarked that on the western slope of the Wahsatch 

 range, in Utah, these concretionary nodules were very common in 

 the granites. Tunnels showed that they did not extend deep into 

 the rock, but occurred only near the point of contact with other 

 rocks. 



