ASSOCIATED METAMOKPHIC HOCKS OE THE LAKE-DISTKICT. 583 



It would seem, then, that the only alternative to this mode of 

 considering the relationships of the granites under consideration is 

 to believe that granite may be formed, or may have been formed, at 

 a depth of 14,000 feet, and that the measurements of the liquid- 

 cavities and their vacuities are delusive and of no value. 



Mr. Sorby, who has very kindly glanced through these pages, is of 

 opinion that the suggestion given above as to the Snap Granite 

 would be quite satisfactory if we could assure ourselves that, when 

 the rock was driven into its present position, the quartz was suffi- 

 ciently solid to withstand the pressure resulting from the enclosed 

 heated liquid, or the temperature at the same time reduced. 



4. Ennerddle and Buttermere Syenite and Syenitic Granite. — This 

 rock might be regarded in part as a syenitic granite, since it contains 

 quartz as well as hornblende, though the mica is often absent and the 

 hornblende very variable in quantity. Itforms awide spread, ranging 

 north and south for about 9 miles, and adjoining the Eskdale Granite 

 at the foot of Wastwater. Through a large part of its course it forms 

 the boundary between the Yolcanic Series and the Skiddaw Slates, 

 but in the south occurs wholly amongst the volcanic rocks. Both 

 Skiddaw Slates and Volcanic beds are much altered in its neighbour- 

 hood, the alteration sometimes extending to a distance of more than 

 a mile from the mass. In appearance the rock is very different from 

 the Eskdale Granite, though the quartz is generally interstitial and 

 not crystallized, and the hornblende is small in quantity. 



The value of v in the liquid- cavities of the quartz in this rock is 

 greater than in any of the other cases (see table, p. 575), being -190. 

 This, at a temperature of 360° C. (680° P.), indicates a pressure of 

 35,000 feet in rock. The lowest temperature at which solidification 

 could take place, supposing p = 0, is 267° C. (512° P.). 



The question now arises whether we can consider this wide-spread 

 mass to bear any direct relation, as source, to the Yolcanic Series. 

 I have stated my reasons elsewhere* for believing this not to be the 

 case ; the beds of lava are not apparently such as would proceed from 

 such a source, although much of the ash is markedly felsitic. If the 

 mass does represent a source of volcanic products, it must, as we now 

 see it, have furnished materials for the uppermost beds of the series 

 only ; and in that case the depth at which the rock became consoli- 

 dated was probably very slight, — but a few thousand feet. If this 

 be so, then the value of v should, theoretically, be much greater than 

 .190, and, if microscopic results be worth any thing, should more 

 closely approximate to that yielded by the quartz in the trachyte of 

 Ponza, which has been shown by Mr. Sorby to be -3, indicating a 

 pressure of 4000 feet at a temperature of 360° C. (680° P.). 



Granting, however, that the microscopic results are of some value, 

 the observed value of v in the case of the Ennerdale Syenite shows 

 a pressure of 35,000 in feet of rock ; and, if not consolidated under 

 merely a few thousand feet of rock, it may be referred with proba- 

 bility to about the same period as the formation of the Eskdale 



* Official Memoir on the Geology around Keswick. 



