OPPONENTS AND OBJECTIONS. 203 



fact, that it was preserved by the introduction of serpentine at 

 the time of its growth. Above the unbroken Eozoon reefs are 

 limestones made u.p apparently of the debris of Eozoon thus 

 )reserved by serpentine, and there is no doubt that this cal- 

 [•eous rhizopod, growing in water where serpentine was not 

 process of formation, might, and probably did, build up pure 

 lestone beds like those formed in later times from the ruins 

 )f corals and crinoids. Nor is there anything inconsistent in 

 lis with the assertion which Messrs. King and Rowney quote 

 )m me, viz., that the popular notion that all limestone forma- 

 ms owe their origin to organic life is based upon a fallacy, 

 ^he idea that marine organisms originate the carbonate of 

 le of their skeletons, in a manner somewhat similar to that 

 which plants generate the organic matter of theirs, appears 

 be commonly held among certain geologists. It cannot, 

 lowever, be too often repeated that animals only appropriate 

 le carbonate of lime which is furnished them by .chemical 

 jtion. "Were there no animals present to make use of it, 

 Lbe carbonate of lime would accumulate in natural waters till 

 these became saturated, and would then be deposited in an in- 

 )luble form; and although thousands of feet of limestone have 

 ieen formed from the calcareous skeletons of marine animals, 

 it is not less true that great beds of ancient marble, like many 

 modern travertines and tufas, have been deposited without 

 the intervention of life, and even in waters from which living 

 organisms were probably absent. To illustrate this with the 

 parallel case of silicious deposits, there are great beds made 

 up of silicious shields of diatoms. These during their lifetime 

 extracted from the waters the dissolved silica, which, but for 

 their intervention, might have accumulated till it was at length 

 [^deposited in the form of schist or of crystalline quartz. In either 

 ise the function of the coral, the rhizopod, or the diatom is 

 limited to assimilating the carbonate of lime or the silica from 

 Its solution, and the organised form thus given to these sub- 

 bances is purely accidental. It is characteristic of our 

 Iknthors, that, rather than admit the limestone beds of the 

 iozoon rocks to have been formed like beds of coralline lime- 

 bone, or deposited as chemical precipitates like travertine. 



