90 Outlines of Geology . 



once, and plausibly fix upon the deluge. I leave the proofs of such 

 irresistible and extended currents to future lectures ; but of their 

 general agency, the instance of intersection and denudation to 

 which I have alluded affords strong confirmation ; for it sometimes 

 happens that in insulated hills, in outliers, as geologists sometimes 

 call them, we discover, although at a considerable distance from 

 the chain with Avhich they were once connected, some of the lower 

 ranges of those strata, the upper ones having been washed away. 



But although we find it necessary to refer, for satisfactory ex- 

 planation of much that we now see, to that period when the earth 

 ** was covered with the deep as with a garment," and when " the 

 waters stood above the mountains," it is by no means intended to 

 exclude altogether the influence of later and partial inunda- 

 tions, of which we shall duly take notice, but which are manifestly 

 inadequate agents to the production of the effects just mentioned. 

 Hence the necessity of a distinction of the terms applicable to them, 

 and the propriety of designating the water-worn fragments, and 

 pebbles, and debris of all the recks, by the term diluvial products, 

 while we limit the term alluvium, to the sandy and muddy col- 

 lections of our present currents : these are seldom carried far ; 

 they form flats and deltas near the mouths of rivers, and accumu- 

 lations of finely-divided matters in their beds ; but of the compa- 

 ratively gigantic force of diluvial currents ample testimonies 

 are extant ; and when we find pebbles which have obviously been 

 thus transported for many miles, and even huge blocks which 

 have suffered a corresponding transplantation and attrition, and 

 lodged in valleys separated by lofty ranges of hills from the rocks 

 whence they must have had their origin, we may not only form 

 8ome idea of the force of the torrent, and the power of attrition 

 of the substances impetuously hurried along by it, but we also 

 read in such phsenomena the most unequivocal evidence of the 

 non-existence of many of the deepest valleys and most striking 

 irregularities of surface which now exist, at the time that the 

 boulders and pebbles M'^ere transported. 



Several geological hypotheses, and the Huttonian theory in 

 particular, affect -to descry, in the agency of existing causes, the 



