304 SEKPENTINE AND ASSOCIATED ROCKS IN ANGLESEY. [May 1 899. 



exterior of a mass. The origin of the dykes of enstatite-rock and 

 diallage-rock had been carefully considered, and for reasons given 

 the Authors were convinced of their intrusive character. As regards 

 the somewhat local character of the crushing, that was undoubtedly 

 true of Anglesey as of other regions of great earth-movements. 

 Serpentine often exhibited this peculiarity in the Alps : he thought 

 probably because, as the rock was brittle, the outer part gave way 

 and saved the rest. To Prof. Sollas, he replied that he also had 

 been often struck with the similarity of igneous rocks of different 

 ages, and it was very true of serpentines. He could not believe it 

 possible that pieces of glass could have been preserved in a holo- 

 crystalline peridotite. He fully agreed in the importance of chemical 

 analysis, but thought it of minor value where, as in this case, rocks 

 had been greatly altered. To Prof. Seeley, he pointed out that the 

 sharply-defined boundary of the spherulite would be consistent with 

 almost any theory of its origin ; and in answer to Gen. McMahon's 

 request for a theory of the origin of the varioles, he briefly 

 summarized that which he had given in his outline of the paper. 



