238 PBOCEEDISTGS OP THE GEOLOGICAL SOCIETY. [Nov. 16 



that their degree of metamorphism bears in several tracts a close 

 relation to the amount of granite which has been intruded among 

 them, and that thus the eastern rocks which overlie the western 

 deposits have been rendered more crystalline than those of older 

 date. At the same time there are wide tracts of country where the 

 upper or flaggy gneiss is in a highly crystalline state, and yet where 

 the observer is unable to detect any granite, porphyry, or other 

 purely igneous product in the proximity. For, after all, such erup- 

 tive rocks are merely to be viewed as the occasional signs of the 

 effusion of that great internal heat, which may have accompanied 

 the metamorphosis of a whole region of stratified rock without being 

 the sole, or even the main cause of the great change, which pro- 

 bably resulted from a combination of electrical and other forces. 



Hypothetical view respecting the gneissose rocks of the Southern 

 Highlands. — Having come to the above conclusions respecting the 

 age of the eastern gneiss of Sutherland and Ross, I venture to 

 suggest that nearly all the eastern gneiss of the counties of Inver- 

 ness, Nairn, Moray, Banff, and Aberdeen, as well as many stratified 

 rocks of the Southern Highlands, may prove to be younger than 

 the fossiliferous quartz-rocks and limestones of the North- west. 



Not having carefully examined the chain of the Grampians, I 

 cannot pretend to say that some of the fundamental gneiss and older 

 granite may not be there partially exhibited. But I hold it to be 

 highly probable that the so-called gneiss which ranges along the 

 edges of the Old Bed Sandstone of Moray and Banff, and is seen 

 on the banks of the Spey where crossed by the railroad, and thence 

 extends to the east coast, belongs to the younger gneiss, and that 

 the micaceous flags (not slates) east of Fochabers, and the clay- 

 slates extending from Foundeland to the tracts south of Huntley, 

 are simply different members of the same Lower Silurian strata. 

 The clay-slates are, indeed, so little metamorphosed, that I cannot 

 but believe that Graptolites or other fossils will some day be found 

 in them. Again, on the eastern flanks of the Grampians, wher- 

 ever I examined these clay-slates, I found them to be simply thin 

 argillaceous flags, void of cleavage, with - intercalated courses of 

 limestone; nor could I comprehend how, by the smaller or larger 

 quantity of mica, great lithological distinctions could be maintained 

 along definite zones, — so much does one of these classes of rock 

 graduate into the other. Furthermore, I observed in the glens 

 which enter into the south-eastern flank of the Grampians, various 

 bosses and bands of eruptive porphyry which are marked on no 

 map, but which have doubtless served so to modify the strata, 

 that the transition from one lithological character to another, as 

 from clay-slate to mica-schist, and from the latter into the so- 

 called gneiss, becomes so devious and irregular, that it is almost 

 impossible to lay them down in separate zones on any map now 

 extant. 



And here I must take the opportunity of again expressing an 

 opinion which I put forth at the Glasgow Meeting of the British Asso- 

 ciation in 1854, and which has been reiterated in the last edition of 

 ' Siluria,' and also in my last communication to this Society. It is, 



