248 Prof . Sedgwick OH the Origin [April,. 



facts above stated may be found in every country which is simi- 

 larly circumstanced with that which has been described. My 

 object is not, however, to make out a new arrangement, but to 

 confirm an old one ; I shall, therefore, content myself with 

 referring to one additional class of examples. 



In many parts of Cornwall the flanks of the central chain of 

 hills are covered with a thick deposit of diluvial gravel, which, 

 after resting immediately on the granitic and schistose rocks of 

 the country, and following their inclination, often descends into 

 the lower part of the transverse valleys, and from thence shelve 

 down below the level of the sea. Near the mouths of these 

 valleys the diluvium is always covered up by beds of a more 

 recent detritus which in some places are nearly sixty feet thick. 

 Notwithstanding their great thickness, many large excavations 

 have been made through them for the purpose of extracting the 

 tin ore which has been washed down from the mountains at the 

 time the diluvial rubbish was formed, and which (in consequence 

 of its great specific gravity) has naturally subsided to the bot- 

 tom of the formation. In various excavations of this kind 

 (provincially called stream-works), conducted in different parts 

 of the county, we may see in the clearest manner the true rela- 

 tions of the several superficial deposits; and (as far as any thing 

 can be proved by single instances) thesectionsshow; first,thatall 

 the diluvial detritus in that part of England originated in tlie 

 same system of causes which, having produced their effects 

 once, were never repeated ; * secondly, that all the alluvial 

 detritus, of whatever kind, is posterior to the preceding ; 

 because it constantly rests upon it, and never alternates with it. 



By the examination of facts like these, we become acquainted 

 with the natural history of such superficial deposits as I have 

 been describing. The facts are in strict accordance with every 

 thing which I have myself observed, and they are, 1 believe, in 

 accordance with the observations of all English geologists who 

 have personally examined the evidence connected with this sub- 

 ject. We may therefore conclude on an induction founded on 

 a very wide range of consistent observations ; 1 . That alluvial 

 deposits include a large class of formations which have originated 

 in causes such as are now in daily action ; 2. That the same 

 causes have acted during a long period ; 3. That during that 

 period the deposits have not been niterrupted by any catastrophe 

 which has interposed any other deposits of a distinct character ; 

 4. That diluvial deposits possess a distinct character from the 

 preceding class, never alternate with them, and, from their posi- 

 tion, evidently belong to an older epoch ; 5. That during the 

 epoch in question, the diluvial gravel was produced by extraor- 



* This fact is of great importance and was, I believe, first remarked by Townsend 

 in bis " Vindication of Moses." (See vol. i. p. 227, &c.) I had repeated opportunities 

 of verifying this remark during a tour in Cornwall made in the summer of 1819. 



