492 MR. J. B. HILL ON PROGEESSIVE METAMORPHISM [Aug. 1 899, 



corundum. Allusion has been made to this fact here, as the -well- 

 known contact-minerals cordierite and sillimanite were found by 

 Mr. Teall in rocks obtained from the aureole of contact-alteration 

 of the Glen Fjme granite, described in the Geological Survey memoir 

 on Cowal. 



Age. — When we attempt to assign a geological age to the members 

 of the Dalradian Series herein described, we are confronted with the 

 difficulty that these beds have up till now failed to yield any organic 

 remains that can help us in their determination. In the absence of 

 such assistance we can only ascertain their stratigraphical position 

 in reference to fossiliferous strata which occur among them. 

 What we do know is that they existed as crystalline schists before 

 the epoch of the Old Red Sandstone, for pebbles of the schists are 

 found in the conglomerates of Lower Old Red age. It will be well, 

 however, to bear in mind the existence of important masses of pre- 

 Cambrian sediments, now well known in Scotland as Torridonian, 

 in Britanny as Brioverian, and in America as Algonkian and 

 Huronian ; and it is probable that these sediments may also 

 eventually prove to be of pre-Cambrian age ; but in the present 

 state of uncertainty they have conveniently been referred to as 

 Dalradian. 



Discussion. 



Sir A. Geikie said that he had gone over the ground described in 

 this paper with the Author, and had satisfied himself that the main 

 fact upon which the latter insisted was undoubtedly true — that 

 around Loch Awe the strata had escaped metamorphism into the 

 schists that formed most of the Highlands. These strata are so little 

 altered that they might be mistaken for Silurian sediments, and he 

 did not despair of their yet proving fossiliferous. But they become 

 progressively more highly metamorphosed as they are followed 

 towards the north-east, until they pass into the ordinary Dalradian 

 type of schists. Many points of extreme interest in regard to the 

 general question of metamorphism and to the structure and origin 

 of the Highland schists arose out of the facts dealt with by the 

 Author, who had been engaged for several years in the investi- 

 gation of the Loch Awe region, and had mapped it with much 

 skill. It was an important step in the investigation of High- 

 land geology to discriminate, so clearly as he had done, several 

 distinct stratigraphical groups, to demonstrate their sedimentary 

 origin, and to show their gradual lateral passage into true schists, 

 apart altogether from the effects of any visible mass of intrusive 

 rock. The Author had recently been transferred to Cornwall, 

 where his training in the Argyllshire region would prove of great 

 service in unravelling the complicated stratigraphy of that part 

 of the United Kingdom. 



Mr. G. Baerow observed that the area here described is of special 

 importance, as the rock-groups to which reference is made have been 

 traced continuously, along the line of strike, right across Scotland. 

 :ft has been remarked that, as these rocks enter the area permeated 



