320 



PEOF. T. G. BONNET ON THE 



Two other points of yet wider interest claim our special attention. 

 One is the remarkable lithological similarity between many of 

 the above-described rocks and those which in other areas are, with 

 more or less certainty, identified as Archaean. The banded gneiss of 

 the Pouldu and of Roscoff,especially the latter,constantly reminded me 

 of the more typical members of the " granulitic " series at the Lizard. 

 Both also, but especially the former (where the results of pressure 

 are more marked), sometimes recalled some members of the " newer 

 gneiss" of the Highlands, especially those which occur some distance 

 away from the northern outcrop. Both, again, often reminded me of 

 some of the finer-grained rocks among the indubitable Hebrideans 

 of Gairloch and the Laurentians of Canada. In some parts of Brit- 

 tany (as at Quimperle) I was also reminded of the coarser gneisses 

 in the last-named country, of the coarser Hebrideans of Scotland, 

 and of rocks which, in the Alps and elsewhere in Europe, are believed 

 to be their representatives. Sometimes, moreover, I observed mica- 

 schists, which might be matched in the Alps, in Scotland, and other 

 European localities. Dr. Barrois and other French geologists con- 

 sider these Breton rocks to be Archaean, and I cannot doubt that 

 they are right. It may be wiser to abstain at present from specu- 

 lation as to the significance of these coincidences, but at any rate 

 they are facts which must have some meaning, and which it would 

 be unphilosophical to ignore. 



The other point is the close geological resemblance between 

 Brittany and the south-west of England. In each district we have a 

 mass of Palaeozoic sediments, up to the Carboniferous, resting on a 

 floor of Archaean rocks. Each district has been affected by great earth- 

 movements, of which the most clearly marked in either, at the 

 present time, seems to have closed the Carboniferous epoch of sedi- 

 mentation. Each, omitting minor flexures, forms a broad synclinal ; 

 between these was an anticlinal, now occupied by the sea, from 

 which only a few fragments of the basal rock-masses project. To 

 the north of the English districts is another anticlinal, occupied by 

 the Bristol Channel, followed by the synclinal of the South-Wales 

 Coalfields. Hence, towards the end of the Palaeozoic period, a great 

 Highland mass must have existed in this Eranco-British region, 

 which, even if we leave out of consideration the South- Wales area, 

 was not less than 300 miles wide across the general strike of the folds. 

 To its altitude we have no clue, but its breadth must have exceeded 

 that of the Alps*, and probably it extended westward beyond the 

 south-western angle of Ireland, while traces of it can be followed 



position, en quelque lieu du globe qu'on l'observe. Ce n'est que par une exten- 

 sion tout a, fait abusive de l'idee du rnetamorphisme qu'on a pu penser parfois 

 a supprimer les schistes cristallins de la serie chronologique, pour n'y voir 

 qu'une modification capable d'affecter des sediments d'age quelconque. Pour 

 tout esprit non prevenu, les fait observes en Bretagne nous semblent de nature 

 a donner le coup de grace a cette maniere de voir." 



* The breadth of the folds, and the not unfrequent absence from considerable 

 parts of the district of a marked cleavage-foliation at a high angle, suggests 

 that the vertical elevation of the chain may have been less, comparatively speak- 

 ing, than in the Alps. 



