204 Dr. Mac CuUoch on the Origin, Materials, 



operations of animals, the quantity of calcareous earth deposited 

 in the form of mud or stone is always increasing ; and that, as 

 the secondary series far exceeds the primary in this respect, so, a 

 third series, should one hereafter arise from the depths of the sea, 

 will exceed the last in the proportion of its calcareous strata. It 

 will combine the ruins of the last limestones with the spoils of the 

 present animals ; animals, of which the generations are also pro- 

 bably enlarging and extending in every age, in a ratio propor- 

 tioned to the increase of those calcareous or soft alluvial and sub- 

 marine deposits which they affect and favour. Those who, like 

 Dr. Hutton, extend the prophetic eye of philosophy to worlds yet 

 unborn, may also thus anticipate a constant and steady approach 

 to that universal state of fertility which is now the pride and 

 character of our calcareous soils^ 



If we now turn our views backwards to the primary rocks, we 

 find, in the disproportion of their limestones, a confirmation of this 

 opinion respecting the important agency of living animals in the 

 production of calcareous strata. It has always been believed by 

 geologists, that no animal remains existed among the primary 

 rocks ; and to avoid a breach in this hypothesis, among other 

 reasons, the transition class was invented. I shall not here dis- 

 cuss the truth or the utility of this invention. It is sufficient to 

 say, that the schists containing shells are consecutive to those 

 rocks admitted to be primary, and that the only general revolu- 

 tion among the strata which we know, is of a later date than 

 these. So far, therefore, as the present purpose is concerned the 

 animal remains of the schists are primary, in as far as they are 

 prior to the secondary strata. Nevertheless, the animal remains 

 of the primary strata, admitting those now named, so as to give 

 the most favourable colour to the subject, bear a disproportion to 

 the whole of the rocks, not unlike that which the limestones do 

 to the siliceous and argillaceous strata. This should be expected 

 from the rarity of these animals in the ancient ocean. 



It has been supposed by some geologists, that all the calcareous 

 strata, of whatever age, were the exclusive produce of animals. 

 That possibility is countenanced by the phenomenon of the coral 



