148 DEPOSITS REFERABLE TO SEDIMENT. 



abundant vapours, could then support the same organic creatures ; here we 

 have the reason why mineral beds, of a determined age, differ less in the 

 organic remains they contain, wherever found, than existing creatures of 

 different zones. 



DEPOSITS REFERABLE TO SEDIMENT. 



S. Rolled flints, sand, and mud, are formed by the action of 

 running water and of waves ; and, being transported by these 

 waters, they accumulate in lakes, in seas, at the mouths of rivers, 

 and on coasts. Whenever we find these kinds of matter accumu- 

 lated in more or less considerable deposits in the interior of coun- 

 tries, we have a right to conclude that there existed somewhere, far 

 or near, high mountains, from which these matters were detached ; 

 water-courses, which carried them ; undulating waters, which 

 heaped them up on their shores, and often lakes and seas, that 

 received them. By the greater or less abundance and size of the 

 rolled flints, we can judge of the mass and force of the waters that 

 transported them; and their nature, and various course or track, 

 ought to lead to the point of their origin, if circumstances have not 

 destroyed the traces left by currents in their course. 



As in the present day we see deposits of shells formed in lakes and seas, 

 we infer that the numerous beds of the same kind we find at all heights, 

 even on the summits of the loftiest mountains, were necessarily formed 

 under water ; the nature of the organic remains enables us to determine 

 whether they were deposited under fresh or salt water, on coasts or in depths 

 of the sea; their mixture, their alternation, indicate mouths of rivers, alter- 

 nations of salt and fresh water, &c. 



4. Deposits from fresh water. These deposits are easily re- 

 cognised from the organic remains they contain being comparable 

 to different genera, sometimes even to different species of animals 

 now living in our lakes and rivers. These are especially remains, 

 impressions, or moulds of shells, like those of the genus limnc'a 

 (Jig. 227), planor'bis (fig. 228), paludi'na (fig. 229), mela'ma 

 (fig. 230), and of knd shells of the genus helix. These are all 



Fiff. <227.Limne'a Fig. 228.- Plnno'rbis Fig. 229. Paludi'na Fig. 230. Mela' 



Lmgisca'ta. euom'phalus. lenta. nia inquina'ta. 



3. How are rolled flints formed ? What does the presence of a deposit 

 of rolled flints in a country indicate ? What is inferred from their size and 

 quantity ? 



