378 ON THE ALLUVIAL DEPOSITS. 



of no modern rock thus generated : nor has any ex- 

 tensive mass of rock, produced by rust, been described, 

 though partial conglomerates of this nature, occur in 

 gravel beds, on sea shores, and in places where ferru- 

 ginous springs flow through loose materials ; as I have 

 also found conglomerate veins produced in this man- 

 ner in Scotland. 



The only alluvial rocks which demand notice for 

 their own intrinsic interest, are those produced by car- 

 bonat of lime. Of these,.there are two distinct cases ; 

 both of them interesting, from the extent of the pro- 

 duce, the errors to which they may give rise, and the 

 illustrations which they afford respecting the antient 

 strata. 



If the important strata formed from fragments of 

 coral, enabling these islands to surmount the highest 

 rise of the ocean, demand no further notice, the similar 

 productions so extensively generated in the West In- 

 dian islands, and, in the Bahamas and Bermuda most 

 conspicuously, produce modern oolithes resembling 

 those of the antient strata. If the want of observa- 

 tions does not enable us to decide on the present value 

 or effects of these productions, we cannot doubt that 

 extensive strata are thus forming in these regions ; 

 while under the processes of elevation already sug- 

 gested, whether gradual or sudden, it is easy to ima- 

 gine the importance of the results, in the production 

 of a supramarine and calcareous territory. Of the 

 analogous rocks produced on sea shores in Europe, 

 those of Messina offer an example well known from 

 their extent and their ceconomical uses. 



The other case, remaining for notice, is the produc- 

 tion of calcareous rocks, at the present day, and also 

 in the times of the alluvial deposits, from solutions of 

 carbonat of lime alone. If the formation of stalac- 



