in the Neighbourhood of Edinburgh. £61 



with those belonging to an upper stratum. Thus, for instance, 

 the Burdiehouse limestone has a character essentially different 

 from that of Wardie, which forms a higher stratum. 



It is easy to suppose that, in the change which would cause 

 a fresh- water lake to sink beneath the depths of the ocean, and, 

 vice versa, to emerge and resume its fluviatile character, many 

 races of animals, limited to definite conditions of water, must 

 have been destroyed. But it would also appear, that their place 

 has been supplied by successions of new races. 



In the next place, a state of the earth's surface, subject to 

 oscillatory movements, may afford an argument relative to ano- 

 ther question which has been started. It has been supposed, 

 from certain a priori reasonings, that during the carboniferous 

 epoch, the air was so filled with carbonic acid gas as to be un- 

 favourable to the respiration of animals possessing lungs. And 

 hence it has been maintained, that no saurian animal during this 

 period could subsist. If, however, the Megalichthys is really al- 

 lied to the Lepidosteus, the researches of M. Agassiz have shewn 

 that recent sauroid fish possess not only lungs, but likewise a 

 trachea, and a glottis. The argument, therefore, of the air having 

 been so filled with carbonic acid gas as to be fatal to the respira- 

 tion of reptiles which possess lungs, becomes at least suspicious. 



The question, therefore, remaining is to the following ef- 

 fect : If the Megalichthys, in common with the Lepidosteus, has 

 possessed lungs, to what condition of the earth's surface might 

 these lungs bear reference ? The solution of this question can 

 perhaps only meet with a satisfactory solution by an appeal to 

 the actual habits of the recent Lepidosteus, which dwells among 

 the large lakes of South America, but of which I can find no 

 written account whatever. 



In the absence of this information, it may perhaps be allow- 

 able to throw out a conjecture with regard to the oscillatory 

 movements, which were going on upon the earth's surface during 



