490 MR. J. B. HILL ON PROGRESSIVE METAMORPHISM [Aug. 1899^ 



Melfort, and making their appearance again on the coast of Locb 

 Fyne. The Ardrishaig beds at Loch Melfort and the Loch Awe bed» 

 are in their least altered condition. As we approach Loch Fyncv 

 however, towards the sonth-east a very different type of meta- 

 morphism prevails, and the Ardrishaig beds where they occur on 

 Loch Fyne are true crystalline schists, in vivid contrast with their 

 unaltered character to the north-west at Loch Melfort. So that 

 here, although the metamorphism is increasing across the strike, we- 

 see the same series of rocks coming up again in another area in two 

 very different conditions of metamorphism. 



In the neighbourhood of Loch Fyne it can also be shown that 

 the Ardrishaig Series presents a gradually increasing type of 

 metamorphism in a north-easterly direction from Ardrishaig ; 

 this increasing metamorphism, though gradual, becomes much 

 more rapid as we reach the flanks of Beinn Buidhe, 6 miles 

 north-east of Inveraray, where it is accompanied by intense folding^ 

 as well as induration, the dips, which hitherto have been steady 

 to the north-west, being in parts of Beinn Buidhe so confusing 

 that in some localities even a general dip cannot be ascertained. 

 In this case it may be noted that we are approaching the area 

 of the Glen Fyne granite, bosses of granite, diorite, and monzo- 

 nite being of frequent occurreuce in this highly indurated and 

 altered area. Some hornfels occurs on Beinn Buidhe very similar 

 to the hornfels on the flanks of Ben Cruacban, and we may assume 

 that the hornfels, at any rate, has been produced by the igneous 

 masses which are connected with the Glen Fyne granite.^ In this 

 case we are dealing with progressive metamorphism along the strike, 

 in which the beds where least altered are in the condition of crystal- 

 line schists. Phenomena of a similar nature have been described by 

 Messrs. Gunn, Clough, and myself in the ' Geology of Cowal,' where- 

 it has been pointed out by us that the garnetiferous mica-schists, 

 which succeed the xirdrishaig Series to the south-east, gradually 

 increase in metamorphism along the strike in a north-easterly 

 direction ; but here, also, we are dealing not with comparatively 

 unaltered beds, but with rocks which are already in the nature of 

 schists becoming more crystalline. 



Progressive metamorphism crossing the strike of beds has been 

 observed in other portions of the Highlands. My colleague, 



^ [Since this j)aper was read I have revisited the district, and have detected 

 typical hornfelsing in the monzonite-aureoles of Beinn Buidhe. It is inter- 

 esting also to record that my colleague, Mr. R. G. Symes, has recently mapped 

 in the neighbourhood of Kiluielfort some small granite-masses similar to those 

 on Beinn Buidhe, and producing similar hornfelsing. The occurreuce of this 

 hornfelsing, in the midst of the unaltered Loch Awe beds and many miles distant 

 from true crystalline schists, greatly strengthens the view advanced in the present 

 paper, that the granites of JBen Cruacban and Beinn Buidhe have effected con-- 

 siderable contact-metamorphism apart from the regional type which surrounds 

 them. It may be noted that the hornfelsing at Kilraelfort has not been 

 observed in the shales of Lower Old Red Sandstone age, but only in the older 

 rocks of the Loch Awe Series into which the granites have protruded. — Julyl2thf 

 1899.] 



