ALLUVIAL DEPOSITS OF TWO DISTINCT ERAS. 
185 
EVIDENCE OF DILUVIAL ACTION AFFORDED BY 
DEPOSITS OF LOAM AND GRAVEL. 
It is admitted on all hands, that the surface of the earth is 
strewed over with deposits of gravel, sand, and loam, which have 
been drifted to their present place by the action of water, since the 
formation of the strata over which these deposits are irregularly 
spread. To account for these appearances, various theories have been 
suggested, all of which have been defective, from their attempting to 
refer to one common cause two distinct classes of phenomena; viz. 
1st, the general dispersion of gravel and loam over hills and elevated 
plains, as well as valleys; and 2d, the partial collection of gravel 
at the foot of torrents, and of mud at the mouths and along the 
course of rivers. The former of these I shall endeavour to show are 
the effects of an universal and transient deluge, the latter are clearly 
referable to the action of existing causes. I know not any work in 
which this distinction is so well and so clearly laid down as in a 
paper by Mr. Bald, (in the third volume of the Wernerian Memoirs, 
p. 123, and fourth volume, p. 58), in his account of the Clackmannan 
Coal Field; in which he says, “The alluvial cover which rests upon the 
rocks of this district is of two very distinct kinds, which are termed 
the old and the recent alluvial coversand this observation, he adds, 
applies to every district of Great Britain which he has examined: 
“ that termed recent is found along banks of rivers and lakes, and is 
generally very fertile ; and along the Frith of Forth is in some places 
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