ANNIVEKSAHY ADDHESS OF THE PRESIDENT. Ivii 



of the earthquake. It may, by throwing a feeble weight into the scale 

 of force, determine the time of the occurrence, but we must look to 

 other and far mightier changes of pressure for the efficient means 

 whereby the earth is made to feel the dread Typhoean agony. 



In applying the knowledge we actually possess from the study of 

 special cases to the general problem of the metamorphism of gneiss 

 and other associated rocks, we shaU. be obliged to consider also the 

 theory of the origin of granite and other unstratified rocks, which, in 

 masses of various dimensions, often show themselves in the metamor- 

 phic regions. If we take a general view of the region of Cornwall 

 and Devon (one of the best known countries in this respect, and yet 

 in other respects one of the least known), we shaU find the granite 

 of Dartmoor, Bodmin, Godolphin moors, and the Land's End, wrapped 

 round by the stratified rocks, and these generally dipping away from 

 the granite*. Near the junction of the stratified and unstratified 

 rocks are many excurrent granitic veins and many traversing elvan- 

 dykes, and in some parts bands of hornblendic rocks foUow the 

 sweep of the strata. 



I suppose no one doubts in accepting these granite-bosses as the 

 summits of a great, perhaps continuous, mass of iuterior rock, ele- 

 vated at a point of time since the date of the carboniferous strata. 

 Collectuig the evidence bearing on the condition of the rock when 

 erupted, it would seem that it had been liquid after the deposition 

 of the bordering slaty rocks, but that it may have been in a consider- 

 able degree solidified, before being raised. It seems to be probable 

 that a similar view may be taken of the granitic eruptions of Arran 

 and the district of the Lakes. 



Returning to Cornwall, we find the great unstratified mass of 

 serpentine, in the Lizard, bounded by strata on the north, and partly 

 so on the south. On the south the rocks are metamorphic (horn- 

 blende-rocks and mica-schist). On the north, the strata are not 

 changed near the serpentine ; they do not fold round it, nor dip 

 from it ; their strike would go through the serpentine ; and it appears 

 to me that in the serpentine -mass surfaces and bands are frequently 

 observable, as if they were the remains of stratification. 



It cannot be said in this case that there is evidence of local intru- 

 sion of this mass of rock among the deposits of the palaeozoic seas, 

 either diuing their deposition or after their consolidation. We are 

 therefore left to choose between supposing it to be a pre-existent 

 mass of fused rock, round and against which the " kill as " was de- 

 posited, or regarding it as an originally stratified mass, which has 

 undergone metamorphism at a later period ; but this process would 

 not require or even admit of the pervading action of a very high 

 temperature, for there is no thermal effbct on the border. On ex- 

 amining the rock chemically, and finding it to be a hydrosilicate of 

 magnesia, we seem to be reduced to the supposition that this is a 

 case of metamorphism in presence of water, if not wholly by the 

 agency of watery solutions. Perhaps the diallagic rocks which 



* An excellent MS. map of the district by Mr. Whitley, of Truro, shows this 

 fact very clearly. 



VOL. XV. e ~ 



