584 



J. CLIFTON WARD ON THE GRANrTIC, GRANITOID, AND 



Granite — close of Upper Silurian, — and the depth at which it was 

 consolidated could not have been greater than that given for the 

 granite, viz. 22,000 feet. 



Whether the difference in appearance and composition between 

 the two rocks be the result of a slightly different depth of consolida- 

 tion, or due to a more immediate connexion with both Volcanic 

 Series and Skiddaw Slates in the case of the syenite, it is difficult to 

 say ; probably the latter has most to do with it. 



Tabulating, as in the former cases, we obtain the following : — 



7. Ennerdale and Buttermere Syenite. 

 v = -190. If jp=0, the min. temp. =277° C. (512° R). 



Sn3 



t 



Top of Upper Silurian. 

 22,000. 



Sorby's estimated temperature of 

 solidification of granites, 360° C (680° 

 F.). 



Fox's calculated 1 temperature at 

 this depth, 259° O. (499° F.)., 



•190 



This gives: 



.'. calculated pressure (j>) =35,000. 



Downward pressure 



r 



22, 



,ra pr 

 J.000. 



Surplus pressure 



t 



13,000. 



5. Quartz Felsite of St. John's Vale. — This rock differs from the last 

 mainly in the quartz being crystallized, instead of being mostly inter- 

 stitial, and in the base being markedly felsitic, though containing 

 porphyritically imbedded felspar crystals. It occurs in connexion 

 with the junction-beds of the Skiddaw and Volcanic Series. The 

 value of v is -170, the pressure corresponding to this being 40,000. 



The arguments used with regard to any volcanic connexion 

 between the Ennerdale Syenite and the rocks of the Volcanic Series 

 apply almost equally well to this case, and need not be repeated in 

 full. Did we find among the volcanic rocks a well-marked series of 

 lavas of the nature of quartz-trachytes or felstones, we might be 

 inclined to regard these masses (not more than 1 mile long) as old 

 volcanic necks ; but in the absence of any such, and in the presence 

 of the evidence furnished by the liquid-cavities in the quartz, it 

 seems more reasonable to conclude that the rock was consolidated 

 under the pressure of the beds of the Volcanic Series and those 

 of the Upper Silurian. 



Thus we have : — I 



