470 ME. J. B. HILL ON PKOGRESSIYE METAMOKPHISM [Aug. 1 899, 



31. On the Peogeessive Metamoephism of some Daleadian 

 Sediments in the Region of Loch Awe. By J. B. Hill, Esq., 

 E.jS"., of the Geological Survey. (Communicated by Sir A. 

 Geikie, D.Sc, LL.D., F.R.S. Eead May 24tli, 1899.) 



[Map on p. 472.] 



Contents. 



Page 



I. Introductory Eeniarks 470 



II. Position of the Rocks in the Highland Series 471 



III. Description of the Ardrishaig Series and the Loch Awe Series 473 



IV, The Intrusive Igneous Eocks of the Area 476 



V. Evidence of Progressive Metamorphism 480 



VI. Conclusions 491 



I. Inteoductoey Eemaeks. 



In the course of the geological survey of the Loch Eyne and Loch 

 Awe districts of Argyllshire, a comparatively unaltered series of 

 rocks was discovered by the author, located in a zone of which 

 Loch Awe forms a central axis. So markedly different in con- 

 dition were they from the ordinary mica-schists of Argyllshire 

 that for some years they were looked upon as considerably later 

 in age than the more crystalline rocks lying to the north and east 

 of them. As the survey of the district progressed, especially in a 

 north-easterly direction, a change of character was detected in them. 

 They assumed a more crystalline condition ; in some areas a gradual, 

 in others a more marked and rapid change of character was observed. 

 In the years 1892 and 1893 it was found that these rocks, as they 

 approached the more mountainous districts of Argyllshire, between 

 Beinn Buidhe and Ben Cruachan, became more highly crystalline, 

 until at last they were traced passing into highly crystalline schists 

 of the normal Central Highland type. 



The results of these observations were briefly set out in the 

 Annual Eeport of the Director-General of the G-eological Survey for 

 the year 1893. on p. 265 of which the present author's work is 

 referred to as follows : — 



* Not less important in its bearing upon the origin and sequence 

 of the Highland rocks is the recent work of Mr. J. B. Hill in the 

 district of Loch Awe, to which reference was made last year. In 

 the course of a recent tour of inspection I took occasion to visit Mr. 

 Hill on his ground, and to examine with him the evidence which he 

 has adduced as to the cessation, or at least the remarkable diminu- 

 tion, of metamorphism, as the rocks are followed from the north-east 

 into the basin of Loch Awe. I was completely satisfied that he has 

 established this statement. I found that in passing westwards we 

 gradually recede from thoroughly schistose rocks, and reach a 

 group of shales and phyllites with bands of limestone, hardly more 



