IN THE MUD OF THE LEVANT. 109 



considerable amount of calcareous matter derived 

 from some other source than the mere breaking 

 up of the Foraminifera, and the raetamorphic 

 condition of which has been produced without 

 destroying the contour of the latter small animals. 

 How far may calcareous excretions have existed 

 here ? At the same time, such strata as the 

 limestone of Santa Fe and the white calca- 

 reous marl of the Pampas seem to indicate, in 

 addition to organic causes, either chemical depo- 

 sition or the extensive instrumentality of some 

 agency that has altered the appearances of the 

 rocks subsequent to their deposition. 



The strata of Magnesian limestone and crys- 

 talline Dolomites, present new difficulties in the 

 way of accounting for the origin of all calcareous 

 rocks by the operation of vital causes. They 

 contain various proportions of magnesia and lime, 

 amounting, in many instances, to as much as 

 45.82 per cent of the former, to 54.18 of the 

 latter.* Now, no organisms that I am acquainted 

 with would have separated these two earths from 

 their state of solution in the sea-water, in anything 

 like the above proportions. Even the bones of 



* Rammelsberg, Handworterbuch der Mineralogie. 



