1868.] ARGYLL ARGYLLSniRE. 2G3 



the question whether granite is not a case of metamorphism earried 

 to the extent of fusion ; nor can it release any geologist who theorizes 

 on a purely mechanical problem from the obligation of reconciling 

 his theory with the observed relations which exist between those 

 rocks which retain all the marks of their sedimentary origin and the 

 granites which, if they ever had that structure, have entirely lost it. 

 It is all the more remarkable that Mr. Geikie should have 

 bestowed so little attention upon this point, since his own general 

 description of the Highlands might have indicated to him the 

 immense significance of any facts bearing on the mutual relations 

 of the granites and the slates. His general description is, that the 

 strata of the Highlands resemble the waves of a sea driven before a 

 N.W. wind. Surely it must occur to every one to ask what was the 

 condition of the strata when they were subject to this subterranean 

 wave-like movement. Were they already consolidated into hardened 

 rock, or were they still in the condition of original deposit, — soft 

 beds of sand and mud? Even in this last case, such movements 

 would in all probability be accompanied by slips or breakages at 

 right angles to the line of motion. Even water when moved in 

 waves "will break at the top, when the line of elevation reaches a 

 certain angle. But if the feilurian strata of the Highlands had 

 already been consolidated into hard and even crystalline rock when 

 this wave-like movement was propelled along them, it is incon- 

 ceivable that it should not have occasioned fractures and dislocations 

 and subsidences of the strata, according to the different degrees of 

 tension which the different beds might be able to bear. Nor is it 

 less certain that, along these lines of fracture and subsidence, what- 

 ever subterranean matter there might be in a fluid or in a \dscid 

 state would find its way to the surface by splashing or protrusion 

 along the lines of least resistance. And yet the geologist who tells 

 us that the crystalline rocks of the Highlands have been actually 

 puckered and crumpled and contorted by subterranean force, never 

 seems to think it worth his while to inquire what evidence on these 

 points is afforded by the structure of the country — whether granites 

 do or do not appear along the lines of fault or of upheavals or subsi- 

 dences of the surface, or whether any facts exist to show the 

 mineral character of the disturbed strata at the time when the 

 fractures were effected. The theory assumes that the country first 

 rose out of the water like some great rounded mud-bank, sloping 

 gently from its summit to the sea, and that along those slopes 

 it was gradually cut and carved into hill and valley by the exca- 

 vating power of mere natural drainage. Mr. Geikie admits, indeed, that 

 ^^ perhaps the elevatory force showed itself in the upheaval of one or 

 more anticlinal folds." But, as usual, admissions which, if followed 

 up into their legitimate consequences, would powerfully affect the 

 argument, are practically set aside almost as soon as made. Our 

 author's favourite illustration of the method in which the river- 

 system of the Highlands was established, is the mode in which a 

 miniature system of streams is made in a bed of wet sand which 

 has been left by the tide. That is to say, the mechanical effect of 



VOL. XXIV. — PART, I. U 



