34 THE CHEMISTRY OF METAMORPHIC ROCKS. [III. 



mens from Scarvig, in Skye ; and the ophiolites of lona resem- 

 ble those of the Laurentian series in Canada. Many of the 

 rocks of Donegal appear to me lithologically identical with 

 those of the Laurentian period ; while the serpentines of Agha- 

 doey, containing chrome and nickel, and the andalusite and 

 kyanite-schists of other parts of Donegal, cannot be distin- 

 guished from those which characterize the altered palaeozoic 

 strata of Canada. It is to remarked that chrome and nickel 

 bearing serpentines are met with in the same geological horizon 

 in Canada and Norway ; and that those of the Scottish High- 

 lands, which contain the same elements, belong to the newer 

 gneiss formation ; which, according to Sir Roderick Murchison, 

 would be of similar age.* The serpentines of Cornwall, the 

 Vosges, Mount Rosa, and many other regions, agree in contain- 

 ing chrome and nickel ; which, on the other hand, seem to be 

 absent from the serpentines of the Primitive Gneiss formation 

 of Scandinavia. It remains to be determined how far chemical 

 and mineralogical differences, such as those which have been 

 here indicated, are geological constants. Meanwhile it is 

 greatly to be desired that future chemical and mineralogical 

 investigations of crystalline rocks should be made with this 

 question in view; and that the metamorphic strata of the 

 British Isles, and of southern and central Europe, be studied 

 with reference to the important problem which it has been 

 my endeavor, in the present paper, to lay before the Society. 



* See in this connection the Essays XIII. and XV. 



