I38 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 894, 



and associated with these are banded gneisses characterized, as a 

 whole, by more micaceous bands, some being fairly rich in biotite. 

 Certain of these gneisses resemble the ' granulitic ' group of the 

 Lizard, and they are spoken of as being occasionally much ' gnarled ' 

 by subsequent earth-movements after the cbaracteristic structure 

 had been assumed. But the most remarkable petrological feature 

 of the island is the occurrence of masses of hornblendite, which 

 are not restricted to any very definite horizon, though they are most 

 common either just above the basement-gneiss or at no great height 

 up in the overlying series. 



In some places large masses of this dark-green hornblende-rock 

 are broken up and traversed by a pale red vein-granite or aplite. 

 The former rock is drawn out into irregular lenticles, elongated 

 lumps, and finally streaks, and has been melted down locally into 

 the aplite, the result being a well-banded biotite-gneiss, agreeing 

 with types which are common amongst the Archaean rocks. The 

 Authors believe, therefore, that Sark presents an example of the 

 genesis of such a gneiss, and they, moreover, are of opinion that 

 probably all the above-named rocks are of igneous origin, but 

 became solid ultimately under somewhat abnormal conditions, to 

 which the peculiar structures (which distinguish them from ordinary 

 igneous rocks) are due. They attribute the banding to fluxional 

 movements, anterior to final consolidation, in a mass to some extent 

 heterogeneous. This hypothesis, they consider, may be applied to 

 all gnehses or schists which exhibit similar structures — that is, to a 

 considerable number of the Archaean rocks. 



Apart even from the important change of front exhibited in the 

 last paper with respect to rocks showing ' stratification-foliation,' 

 these communications on the Channel Islands and adjacent main- 

 land are replete with interest to the British geologist. Seen in the 

 light of modern research, there could have been no objection to 

 grouping the several crystalline formations of the Channel Islands 

 under the heading ' Fundamental Bocks.' But when it is remem- 

 bered that the Jersey conglomerates were once thought to be of 

 Triassic and the Jersey rhyolites of Permian age, it seemed safer 

 to consider the whole matter under the heading ' Petrology,' rather 

 than beg the question, as it were, by grouping them with the Fun- 

 damental Bocks. Nevertheless, there can no longer be any doubt 

 as to the Archaean age of most of these crystalline masses, though 

 perhaps all are not agreed as to the precise interpretation of the word 

 ' Archaean.' We seem, indeed, here to recognize a Lower and an 



