302 Dr. Mac CuUoch on the Origin, Materials^ 



abundant in the later, and comparatively rare in the earlier 

 strata. 



The formation of coral islands, proves that enormous and solid 

 masses of calcareous rock are the produce of animals alone; and 

 when we reflect on the magnitude of some of these, we have no 

 reason to be surprised at the extent of those rocks which, among 

 the secondary strata, are composed chiefly of shells. Were we 

 even to suppose that every particle of the largest bed of limestone 

 known, was originally part of the body of a shell, we should, as 

 far as the bulk of the mass is concerned, assume nothing that 

 would not be countenanced by the magnitude of the great coral 

 reef of New Holland. If the most minute animals of creation 

 can thus, by their numbers, execute unassisted works of such 

 enormous magnitude, and, as navigators think, within spaces of 

 time comparatively limited, it is far from unreasonable to believe 

 that the succession through unnumbered ages, of animals so far 

 exceeding them in bulk and in the relative quantity of their cal- 

 careous produce, should have generated all the calcareous strata 

 in the secondary series. 



It is not necessary here to ask whence the calcareous matter 

 has been derived, or to suppose that it is an animal product. The 

 difficulty is, at present, unquestionably insurmountable; but, in this 

 case, it is of no moment. It can fonn no objection to the power 

 of oysters or pectines in producing, by their own energies, a bed 

 of limestone; because the fact, however inexplicable, is ren- 

 dered certain by the generation of coral from sea-water. That 

 very extensive beds of calcareous matter may be produced by 

 animals, and from their remains, is also incontestibly proved by 

 the oolithe limestones, and by those deposits of shell marl so often 

 found in fresh water lakes. In many such cases, in the Highlands 

 of Scotland, it can easily be demonstrated that this is their sole 

 origin ; because we can trace the courses of the streams by which 

 the lakes have been fed, and ascertain that they could not have 

 carried down calcareous matter ; their origin and progress lying 

 among siliceous strata. 



