92 Dr. KiDD on the Mineralogy cf St, David's. 



it would be improper on the present occasion to enter into the par- 

 ticulars or on the defence of those grounds, I think it respectful to 

 the Society to be silent on those points. 



I may however with propriety add, that from communications 

 v\^ith very competent judges, aided by the inspection of specimens 

 which they had themselves collected, it is clear to me that the 

 geological phenomena above described are of very extensive occur- 

 rence. In Jersey and Guernsey for instance, in various parts of 

 Devonshire and Cornwall, in North Wales and Cumberland, in the 

 neighbourhood of Mount Sorrel in Leicestershire, in all these places 

 severally, is found an assemblage of rocks of a decidedly crystalline 

 character, and consisting of hornblende and felspar, associa'.ed with 

 rocks either of a schistose structure or resembling a more or less 

 fine-grained conglomerate, intersected not unfrequently by masses 

 of a porphyritic character, and sometimes passing into serpentine.* 



In the decidedly crystallized rocks of these suites, consisting of 

 hornblende and felspar, the felspar sometimes predominates and is of 

 a red colour, in which case the compound is usually, I believe, called 

 sienite j but the same term seems justly applicable where the horn- 

 blende predominates and the compound is of a black or of a green 

 colour, for the two varieties insensibly pass into each other. 



The opinion which I have here ventured to express of the natu- 

 ral alliance between the various rocks above described is strongly 

 supported by its correspondence with the opinion entertained by 

 M. Godon respecting a similar class of rocks occurring in the 



* The transition of the natural compound of hornblende and felspar into serpentine 

 has been observed ia Cornwall, and is satisfactorily shewn in specimens brought from 

 thence and deposited in the Ashmolc Museum ; and the opinion of the natural alliance 

 of these two rocks is strongly confirmed by the inspection of numerous specimens brought 

 from the coast of Labrador and deposited in the same Museum. 



