44 ON THE REVOLUTIONS OF 



points the whole powers of their imagination, they thought they had 

 effected all in devising a means of answering them. Besides, in ne- 

 glecting other phenomena, they did not always think of determining 

 precisely the measure and limits of those which they attempted to 

 explain. 



This is particularly true in reference to the secondary formations, 

 which form the most important and difficult part of the problem. For 

 a long time naturalists employed themselves very unavailingly in de- 

 termining the superstrata of their layers, and the relation of these layers 

 with those sorts of animals and plants whose remains they contain. 



Are there animals and plants peculiar to certain layers, and which 

 are not met with in others ? What is the species of those which first 

 appear, or which come after ? Are those two species ever found to- 

 gether ? Are there variations in their return ; or in other words, do 

 the first again recur, and do the second then disappear ? Have 

 these animals all lived in the places where their remains are found, 

 or have some of them been conveyed elsewhere ? Do they all 

 exist at present anywhere, or have they been wholly or partly de- 

 stroyed ? Is there a perpetual uniformity between the antiquity of the 

 layers and the resemblance or non-resemblance of the fossils with liv- 

 ing beings ? Is there a similarity of climate between fossils and those 

 of living beings which most resemble them ? Can we determine that 

 the removal of these beings (if there has been any) has been from north 

 to south or from east to west, or by scattering and mixture ; and can 

 we distinguish the epochs of those removals by the layers which have 

 these marks impressed on them ? 



How can we decide on the actual state of the globe if we cannot 

 answer these questions, if we have not sufficient grounds to enable us 

 to determine in the affirmative or negative ? Besides, it is but too 

 true that during a long period none of these points have been abso- 

 lutely cleared up ; in fact, it was scarcely deemed expedient to clear 

 them up previous to the formation of a system. 



Reason why these Preliminaries have been neglected. 

 It may be assigned as a cause of this peculiar neglect, that geolo- 

 gists have all been either naturalists of the closet, who had themselves 

 but very superficially examined the structure of mountains, or mineralo- 

 gists who had not studied in sufficient detail the innumerable varieties 

 of animals, and the infinite complication of their different component 

 parts. The former have only framed systems ; the latter have made 

 admirable observations ; they have in fact laid down the foundations 

 of the science, but were inadequate to the task of elevating the super- 

 structure, 



