54 Granite. 



formed' indicate depths from the surface varying from 

 15,100 to 65,500 feet. From certain passages it is 

 evident that Mr. Sorby considers that gneiss and granite 

 were formed approximately under similar circumstances. 

 I quote this thoroughly philosophical memoir, that the 

 reader may be less startled with the statement, that 

 gneiss and some granites were formed by the metamor- 

 phosis of strata at depths counted by many thousands of 

 feet, and also to give strength to a the assertion, that 

 under such circumstances water was present. 1 



If the above views be correct, though many granites 

 having been completely fused have been injected among 

 strata, and are thus to be classed as intrusive rocks, yet 

 in the main, so far from the intrusion of granite having 

 produced many mountains by mere upheaval, both 

 gneiss and granite would rather seem to be often the 

 results of the forces that formed certain mountain 

 chains. Possibly this result was connected with the 

 contraction of the earth's crust and the heat produced 

 by the intense lateral pressure that, with much move- 

 ment of parts, produced the contortion of vast masses 

 of strata, parts of which, now exposed by denudation, 

 were then deep underground, and already acted on by 

 the internal heat of the earth in a degree proportionate 

 to their depth. 2 



1 See 'Journal of the Geological Society,' vol. xiv., 1858. Sorby. 



2 See Report, Brit. Assoc. 1866, p. 47 : < Address to the Geological 

 Section,' Ramsay. Also an elaborate memoir by Mr. Robert Mallet, 

 ' On Volcanic Energy, &c.,' Trans. Royal Soc., vol. clxiii. p. 147. 



