^^^' 55-] I^ THE EEGION OF LOCH AWE. 471 



altered than portions of tlie Silurian series of the South of Scotland. 

 As might be expected, however, the diminution in metamorphism, 

 though generally progressive, is not uniform, some zones, owing 

 doubtless to their chemical composition, having been less affected 

 than others above and below them.' 



It is proposed in the present paper to describe, in a little more 

 detail, the phenomena which have been set forth in the above report, 

 or, in other words, to prove that a great group of rocks 

 which extend across the greater part of the Scottish 

 Highlands, in the condition of typical crystalline 

 schists, pass along their strike into rocks scarcely more 

 altered than many Palaeozoic sediments. So far as the 

 author is aware, no previous observer has described these rocks. 



II. Position of the Rocks in the Hi&hland Series. 



Before describing these rocks it will be convenient here to give 

 a brief account of their position in the Highland series. 



In the Survey memoir on the Geology of Cowal, by Messrs. 

 Gunn, Clough, and myself, published in 1897, we described in con- 

 siderable detail the geology of that part of Argyllshire which lies 

 between the Firth of Clyde and Loch Eyne. The district dealt with 

 in this paper is a still further prolongation in a north-westerly 

 direction of the Cowal district which it adjoins. As Sir A. 

 Geikie states in the preface of that memoir, the Cowal district 

 ' embraces the south-western extension of the various bands of 

 metamorphic rocks which form the southern edge of the Highlands. 

 Originally most of the rocks ' described in the memoir ' formed a 

 thick series of sedimentary deposits, the geological age of which still 

 remains to be determined. These strata have been found to have 

 undergone a remarkable series of repeated movements. After being 

 thrown into folds and having been cleaved so as to acquire a first 

 system of deformation, they have again suffered a repetition of the 

 process more than once. They consequently present secondary and 

 tertiary, perhaps even quaternary, structures probably due to 

 mechanical movement with accompanying recrystallization. The 

 regional metamorphism thus produced is not uniformly distributed, 

 but seems to increase in intensity both from the south-east and 

 north-west towards a central line, ranging about north-east and 

 south-west, which is an anticline of the foliation. It has not 

 been traced to any intrusion of igneous rock, and is so general 

 and diffused that it can hardly be regarded as in any sense a 

 contact-phenomenon.' In the memoir just quoted we pointed out 

 that the rocks described in the district embraced various schist - 

 bands traversing the region in a north-east and south-west direction . 

 Starting from the schist boundary-fault and proceeding in a north- 

 westerly direction, we first pass over a group of phyllites and pebbly 

 grits with an average breadth of outcrop of 1 mile. Farther north- 

 west, a grauwacke-schist with an outcrop of less than | mile comes in. 

 This is succeeded by the Dunoon Phyllite Series, with subordinate 



