66 Dugald Bell — The " Oreat Submergence.'" 



a "surface current" in the one case became a "bottom current" in 

 the other ? And was this a sudden catastrophe ? With what 

 immense displacements of water, huge "waves of translation," etc., 

 it must have been accompanied ! How did the fine clay (which says 

 " I am a mnd ") escape in such a turmoil ? Or was it — as seems on 

 the whole more likely — a gradual operation, extending, perhaps, over 

 tens of thousands of yeai's ? (We are arguing on the supposition 

 that there was such a submergence and re-elevation, which we do 

 not believe.) Then will Mr. Smith please to remark that in the 

 gradual re-elevation of the land, all his " deep-sea deposits " would 

 successively be placed in the condition of shallow-water and shore 

 deposits again. And if, in his own words, " the shore waves con- 

 stantly agitate the material they come in contact with, washing out 

 the mud and forming gravels and sands " (p. 501), then what chance 

 had his fine clay (which says "Jam a mud") of being preserved — 

 exposed, as it must have been for an indefinitely long period, to the 

 shore waves of the Northern Sea and to the powerful currents that 

 swept to and fro through the Great Glen? We can, indeed, hardly 

 imagine a more unlikely place than Clava for the existence of " still 

 water " at any time, or for such deposits as these fine clays and sands 

 being preserved. 



(4) Touching, in conclusion, on another subject, Mr. Smith thinks 

 "there is ample proof that they [the Boulder-clays of Ayrshire] 

 are marine deposits." From his examination of them he says he 

 is " finding additional proofs of the whole drift formation having 

 been deposited in the sea." We have already expressed a caveat 

 against rushing to conclusions in that matter (Geol. Mag., July, 

 1896), which, though it has not been much attended to as yet, 

 we hereby beg to repeat. The shells, of which " the great bulk 

 occur as fragments, although there are some very good specimens," 

 are found in the usual Boulder-clay (or clays) of the district, and 

 in certain associated sands and gravels, evidently " washes " there- 

 from. These boulder-clays are of the ordinary massive, unstratified 

 kind, showing, it is true, here and there traces of bedding, with 

 thin layers of sand and gravel, as in all other boulder-clays, but 

 no regular and continuous stratification. They take their colour 

 and composition chiefly from the immediately underlying or ad- 

 jacent strata ; but they contain, mingled with the rocks of the 

 district, a considerable proportion of far- travelled blocks from the 

 Highland mountains to the north-west on the opposite side of the 

 Firth. These characteristics, we submit, mark them as undoubted 

 glacial deposits, which cannot be accounted for by the action of 

 shore-ice (thick or thin), pack-ice, icebergs, or floating ice of any 

 kind. Besides, all floating ice requires currents ; and our powers 

 fail us in trying to conceive of a set of marine currents diverging 

 from the West Highland mountains — westward to the Sounds of 

 Lome and Jura ; eastward by the central valley to the Firth of 

 Forth; and south-south-eastward, across the Firth of Clyde to the 

 bays and recesses of the hills in Ayrshire. 



