I860.] JAHIESON DRIFT, ABERDEENSHIRE. 353 



observations elsewhere) the gravel tumbled into undulating ridges 

 of extremely coarse material made up of well-rolled boulders, some 

 of them 4 to 7 feet in length, mixed with large pebbles and shingle, 

 until at the rocky barrier it thinned quite out, nought being left 

 but a few large blocks that seemed to have been too heavy to move 

 further. Likewise the boulder-drift forming the substratum of the 

 moor seems to get thinner as you approach the rocky barrier, as if it 

 had suffered more denudation thereabouts than further east. No 

 difference, however, occurs in its texture; all is of the same quality 

 from one end of the moor to the other. 



Now these features of the gravel seemed to me to indicate that 

 the water which lodged it must have been in much more violent 

 motion in the neighbourhood of this contracted part of the valley 

 than in the open expanse of moor to the eastward ; and the whole 

 features of the locality, the well-washed flank of Culbleen, and that 

 of the opposite Hill of Pannanich seemed to tell of a large body of 

 water passing eastward down the valley, sweeping the narrow 

 gorges bare, and projecting the gravelly debris out into the open spaces 

 below. 



In looking fur such an agency, we find several to choose from, 

 such as — 



1. The bursting of lakes higher up the valleys. These may 



have been temporary accumiilations of water dammed up 

 by glaciers or landslips. 



2. The action of rivers during floods, which may have been 



caused cither by great rains or the melting of extensive 

 masses of snow and ice. 



3. The retreating action of the sea during the emergence of the 



land from the waters of the marine drift. 



I have already said that the well-rounded aspect of the pebbles, 

 indicating long-continued rolling by water, forbids the supposition of 

 one catastrophe doing the whole by the sweep of a sudden wave or 

 deluge passing over the country. And further, as this gravel is found 

 not along a few rivers, but along all that I have hitherto examined, 

 without exception, and likewise along minor streams, I think the 

 first of the suppositions enumerated above becomes highly improba- 

 ble : for it can scarcely be thought that there has been a bursting of 

 lakes in all the water-courses: and, indeed, with the exception of 

 accumulations of water dammed up by glaciers and the like, such 

 bursting or suddenly giving way of a natural lake is an event of the 

 greatest rarity — indeed, I do not at present remember having read 

 of an instance of it. 



In seeking for a cause, therefore, we must have one of general 

 application. 



Now tho long-continued action of the livers themselves, during 

 and after the emergence of the land, is jusl such a universal!} pre-* 

 sent agent as we are in search of. And the arrangement of tin- 

 gravel is. as l have shown, very like what might be expected from 

 a Beaward-flowing current cutting through the previously deposited 

 drift: while the absence of all marine fossils tends further to enhance 



