1868.] ARGYLL ARGYLLSHIRE. 259 



which was a line of ridge and of elevation in the older rocks. The 

 streams of water, or of ice, or of both, which would follow in that 

 depression, would be so guided in their work that the valley would 

 be cut deeper and deeper, until at last, according to Mr. Geikie's 

 theory of erosion, after millions of years, the cutting would reach 

 the slaty rock which originally had been thousands of feet under- 

 ground. That rock, at the point so reached, might be (as regards its 

 own geological structure) not a depression but an elevated ridge. 

 The crown of that ridge would then begin to be cut away, provided 

 the containing walls of the Old Red Sandstone valley continued 

 during further ages to guide and constrain the stream in the same 

 line of cutting. We must now suppose that this guidance continued 

 so long that the underlying slates have been carved and exca- 

 vated into a deep glen. We should then have a glen excavated along 

 the top and out of the anticlinal ridge of an old Silurian hill ; what 

 had once been the bowels of a mountain would thus be one of the 

 containing sides of a valley. And so over the whole area of the 

 Highlands we can suppose that, through the means and interven- 

 tion of an overlying country of sandstone, the underlying beds of 

 slate came to be cut and carved along lines which had not the 

 smallest reference to their own foldings and convolutions. This is an 

 ingenious hypothesis, but it displays only half the ingenuity required. 

 Having called the 01d-E.ed-Sandstone country into existence for the 

 purpose of the hypotheses, we must for the same sake get rid of it 

 again. And not only must we get rid of it, but we must get rid of 

 it in a very peculiar manner. If it were destroyed by the help of 

 new upheavals from below, these new upheavals would establish 

 new lines of drainage through the whole thickness of the strata thej 

 affected, including both the sandstones above and the slates below : 

 and this new system of drainage could not but entirely alter the 

 former system, which had been constructed when the strata were at 

 rest. That new system would come to be in general conformity 

 with the new geological structure given by the last upheaval. But 

 this would never do : what we have to account for, according to the 

 theory, is a country showing no trace of original effects produced by 

 underground movements. We must therefore get rid of the whole 

 sandstone country without any serious disturbance. It must be done 

 very gently, by nothing more violent than what Shakespeare calls 

 " the gentle rain from heaven ; " and yet it must be done so com- 

 pletely that over the whole area of the central Highlands not a frag- 

 ment, not a pebble, of this great sandstone country shall be left 

 behind. And if for this purpose it be desirable to call in the agency 

 of the sea, then we must suppose that the country was just dipped 

 under the ocean, so slowly and so gradually that when every morsel 

 of the sandstones shall have been washed away, the old slates may 

 again be lifted as slowly into the air with the river-system unbroken 

 and untouched, which had been due, not to its own structure but to 

 the structure of other rocks now removed. In this way, and, so far as 

 I see, in no other way, could we account for a country with folded 

 and contorted strata, and nevertheless with a system of hill-valleys 



