184 A SODA-FELSPAK EOCK. 



cent. The hardness was 6 to 7. The specific gravity 2-63. 

 How could such a rock have been formed ? 



Mr. Teall, in his British Petrology, describes a sedimentary 

 rock altered by contact with an igneous rock to which the name 

 of Adinole has been given Adinole has been found by Grerman 

 geologists to contain as much as 7"5 per cent, of soda when in 

 immediate contact with an igneous rock ; the eruptive rock 

 having impregnated the surrounding sediment with a portion of 

 its own material. The spherulitic and concretionary structures 

 at Dinas head under this hypothesis are difficult to account for, 

 as they are generally supposed to indicate a fused rock. Could 

 this rock be a soda felsite or keratophyre ? It is not easy at 

 present to explain its origin, but it is certainly of interest on 

 account of its remarkable composition. 



Maps and a diagram enlarged from a sketch by Sir A. Geikie, 

 Director-Greneral of the Survey, now on your walls shew that the 

 greenstone is intrusive in, and posterior to, this " adinole." Both 

 rocks have undergone such a degree of crushing in many places as 

 to alter their lines of junction. Microscopic sections of the rock 

 have also been shown. In presenting specimens of this " adinole" 

 to the Institution, it is hoped that the members will be led to 

 examine carefully the various coast exposures of greenstone and 

 slate in order to discover whether any rock similar to that at 

 Dinas Head can be found elsewhere in Cornwall. New discoveries 

 may throw more light on the relations of the rock, and help to 

 solve the difficulty. 



Mr. A. F. Hosking's analyses : 



The Alkali is mainly soda; — by titration with acid it 

 represented 9*6 per cent, of soda on the assumption that soda 

 was the only alkali present. The potash in one of these 



