OF THE SEA AND LAND. 25 



It is impossible to assign the mere mode of action 

 in these cases, supposing the general fact admitted. 

 Were such a current now directed against the opening 

 of any given valley, no greater portion can have acted 

 than what was equal in hreadth and depth to its trans- 

 verse section : and, thus, even at the commencement, 

 it is required to open for itself, in one only spot, a 

 parallel, or a dilated, or an enlarging, or a diminishing 

 channel, often of many miles in length. It is sufficient 

 to suggest the impossible progress of such an operation 

 at the great Caledonian valley, or in that section inclu- 

 ding Glen Tilt, which stretches to Brae Mar. I need 

 not proceed: if any one can produce unexceptionable 

 cases, they must be believed : but none has yet been pro- 

 duced, and I know of nothing, even analogous, unless 

 it be the sudden failure and discharge of a lake; while 

 every such current must hav ? e been too brief to produce 

 much effect, as also that could have been but some en- 

 largement of the previous valley, and scarcely of more 

 than was alluvial. 



But I must not omit one argument supposed to af- 

 ford a strong evidence, of such " diluvian" currents ; 

 namely, the scratches or marks of friction, already 

 noticed on rocks where water does not now flow. 

 Many of the quoted instances occur in places where 

 rivers have once run, under the changes already pointed 

 out; while if the others confirm the former existence 

 of currents that could not well have been rivers, they 

 are not competent to prove such movements of water 

 as I have here rejected. I shall enquire further of them 

 presently, as the probable effects of heavy alluvia trans- 

 ported by water under other causes. 



If I need not repeat, that these imaginary currents 

 have been derived from visionary notions of some early 

 conditions in the ocean, so shall I not enquire further 



