PHENOCRYSTS FORMED SOON AFTER REST 399 



rate either for^ or for C,* while, on the other hand, the increase of grain 

 from the nearest possible contact from which to reckon the same (0 at 

 845 feet to 1 inch at 900 feet) will be a maximum. Thus A or C is more 

 than 25.4/30,480, or 1/1,200, and is less than 25.4/16,900, or 1/670. If, 

 suppose this to be A, and remember that there is a zone of some 1,600 

 feet which is of uniform grain, so that x', where the two tangents meet, 

 is less than 30 meters and probably nearer or more than 40, we shall 

 find that the temperature of consolidation of feldspar will be only .283, 

 and that the zone outside of the granite at which the temperature is 

 affected was 21 meters or less. It is hardly possible that the initial tem- 

 perature of the granite should be three or four times that of the consolida- 

 tion of the feldspar with no melting around the margin and so narrow a 

 zone in which the temperature is affected . It will also imply a high degree 

 of the fluidity of the magma, and that the difference of the temperatures 

 initially would be large compared with the temperatures of consolida- 

 tion of the feldspar and the quartz. Here are four improbabilities. 

 Let us try the other assumption that the slope or increasing grain is to 

 be referred to C. This implies a relatively broad contact zone, a natural 

 supposition to make in case of granite. We shall find in this case the 

 ratio of the temperature of consolidation to the initial temperature, .75. 

 This, we see, brings the curve of grain into the form of the curve marked 

 .60 in plate 5. The quartz, if formed, on the whole, later than the feld- 

 spar, will have a more uniform grain. The great coarseness of the feld- 

 spar (that is, E) is dependent upon ^, cj aVu. Now, c is fairly large, 

 but not exceptional for granite, and it is natural to suppose that u and tto 

 were not great, which would also produce a similar effect. This Uo repre- 

 sents the temperature of the granite magma when it is injected above 

 the country rock, and that it should not be great is a natural supposition 

 for a deep-seated rock and would lead us to expect that the magma 

 would be viscous. This is in harmony with the evidence of drag and 

 shearing, though viscous magmas are rather characteristic of " salic " 

 magmas. 



Even with the very meager and imperfect data above given, therefore 

 we seem justified in assuming as probable that this granite was injected 

 under conditions such that the difference in conditions between the 

 magma initially and the country rock was not very great ; that the con- 

 ditions (temperature) of the formation of the feldspar was about twice 

 as near to the initial condition of the magma as to that of the country 

 rock, and that under such conditions the feldspar was distinctly ahead 

 of the quartz, at least in the beginning of its crystallization. It seems 

 also that there was some flowage or orogenic squeezing of the magma, 



Eqs. 10 and 11. 



