CHEMICAL COMPOSITION IN SEDIMENTS 453 
or else have suffered complete recrystallization. The position in the 
quantitative system of 27 of these metamorphosed granitic rocks 
was computed, and they were found without exception to fall in sub- 
rangs represented by numerous examples among massive igneous 
rocks. ‘Their classification is as appears in the preceding table. 
~ A comparison of the magnesia-lime ratios and alkali ratio in these 
granite-gneisses with those in the granites gave the following results: 
MgO >CaO K,0 >Na,0 
In the unmetamorphosed granites...| I out of 105 analyses | 82 out of 105 analyses 
In the metamorphosed granites. .... I out of 27 analyses 14 out of 27 analyses 
None of the metamorphosed granites show alumina in excess of 
the amounts common in many massive igneous rocks. Corundum is 
present in the norm of 8 out of the 27 metamorphosed rocks, but is 
never in excess of 2 per cent. From their chemical composition 
alone, therefore, it would be impossible to distinguish these 27 rocks 
from typical massive igneous varieties. 
Certain rocks described by Teallt as early as 1885 afford an 
example of the dynamic metamorphism of a basic rock without 
notable changes in chemical composition. ‘Two basic dikes traversing 
the more acid gneisses of Sutherlandshire, Scotland, are in part mas- 
sive and in part highly schistose, the schistose portions being so distrib- 
uted as to show that they were not produced by flowing movements 
in the dike before complete solidification, but are the result of regional 
metamorphism. Upon microscopic examination the massive phase 
is found to have the mineral composition and ophitic texture of a 
typical diabase, while the schistose phase is a hornblende schist devoid 
of kataclastic structures but with a perfect parallel structure, which is 
plainly the result of complete recrystallization. The principal 
mineral changes accompanying the development of the schistose 
structure are the replacement of augite by hornblende and the appear- 
ance of some free quartz in the schist. The chemical composition 
of the two rocks, as shown in analyses I and II, p. 454, is almost iden- 
tical. 
1 J. J. H. Teall, Quart. Jour. Geol. Soc., London, Vol. XLI, pp. 133-45 (1885). 
