89 



ist. It is probable from geological evidence that this granite 

 was consolidated at a depth of about 30,000 feet. 



2nd. An increase of 1° for every 49ft. on descending gives a 

 temperature of 360° C. (680° F.) at a depth of 30,900 feet. 



3rd. Microscopic evidence, deduced from examination of the 

 liquid-cavities in the quartz, gives a calculated pressure, under 

 which the quartz was consolidated, at a temperature of 360° C. 

 (680° F.), equivalent to 52, 000ft. of rock. 



4th. As the calculated pressure thus far exceeds (by 22,000 

 feet) that due to the estimated thickness of overlying beds or — 

 what is the same thing — to the estimated depth at which the 

 granite -formation took place; it follows that there must have been 

 a great amount of available pressure to be exerted upon the rocky 

 crust around, and hence we find evidences of folding and contortion 

 of the rocks, and of their upheaval and general metamorphism 

 around the granitic area. 



The case of the Skiddaw Granite will suffice as an example 

 of this mode of treatment. I have elsewhere (Quart. Journ. Geol. 

 Soc, vol. xxxi. p. 568) treated all the other granitoid rocks of the 

 Lake District in the same way, and with very similar general 

 results. There are yet, however, one or two points I should like 

 to call attention to. 



The first of these is the general absence among the liquid- 

 cavities in the quartz of Lake District rocks, of crystals of various 

 salts, such as have been found in plenty in some other districts. 

 Are we to infer from this that the liquid enclosed at the period of 

 the formation of the granites was less saline than in some other 

 cases ? Or is it possible that a more extended investigation would 

 make it appear otherwise 1 Another thing worth noting is the 

 general absence, as far as I have been able to judge, of cavities in 

 the quartzes containing — not water — but liquid carbonic acid 

 which in some other rocks and other districts are not infrequent. 



While thus calling attention to various points connected with 

 the formation of quartz-bearing rocks of the District, I am far from 

 claiming to have examined into the question exhaustively, and 

 would gladly see other workers take up the subject more com- 

 pletely, and either prove or disprove the results already obtained. 



