OF THE SEA AND LAND. 37 



sent in a neighbouring one; but the conclusion is 

 much strengthened when we see tracts of loose mate- 

 rials that have been produced from their destruction. 

 Thus the dark brown trap soils cf the central parts of 

 Scotland, prove the former existence of such rocks in 

 those places : while, when small arid detached portions 

 of the rock arc found scattered about a country, bear- 

 ing such traces of decomposition, the certainty be- 

 comes almost absolute; and thus also are we enabled 

 to approximate, at least, to the former depth as well 

 as extent of the rock which* has disappeared. In the 

 same way, we must believe that the saline sands of 

 the several Deserts are the produce of that " red 

 marl" which still exists in a sufficient number of places 

 to indicate thus much, at least, of denudation in those 

 countries. I need not now, I hope, answer the spe- 

 culation of a well-known Theorist, which asserts that 

 these are the unconsolidated bottom of the antient 

 ocean. Similar also are many cases of alluvia foreign 

 to the substratum, found on gneiss and other rocks; 

 marking equally the denudation of which they are the 

 remains. Among these, are the alluvial gravels which 

 have often been attributed to transportation, antient 

 or recent, as the theory of each observer inclined him. 

 The different cases may not always be easy to distin- 

 guish : but, unquestionably, many of them are the re- 

 mains of rocks which have been demolished under 

 some process of denudation. Such, probably, are the 

 gravel beds of England: but this subject is more par- 

 ticularly examined in the chapter on alluvia. 



England seems to present many indications of that 

 denudation where the loss is so complete that no traces 

 of the strata remain. This at least may be inferred 

 as to many of the upper ones which we might expect 

 to find, where there is nothing to indicate that they 



