TRANSITION ROCKS. 



ledge of the earth's structure, wemust haverecourseto minute 

 investigation. Many have proposed arrangements of the 

 strata, which they, as the authors,have, of course, considered 

 less liable to objection than those for which they were substi- 

 tuting them. In all these arrangements, there has been no 

 one division of the stratified part of the earth, more uni- 

 versally considered false and unnatural, than that of the 

 " Transition class? It has been said to have no natural ex- 

 istence, but to be the mere creation of minds fettered by pre- 

 conceived theories. As an objection to the term "transition^, 

 some have urged that it is one derived from that theory, 

 which affirms, that the rocks of this epoch were formed, du- 

 ring the passage of the globe, from a state unfitted for the ex- 

 istence of organic beings, to one which wascalculated for their 

 preservation. If geologists have, in the course of their in- 

 vestigations, come to any certainty concerning the ancient 

 states of our globe, there is certainly no one doctrine sup- 

 ported by a greater number of facts, than that of progres- 

 sive development. Many remains have been adduced as 

 belonging to beings, which held a place in the zoological 

 scale, higher than was consistent with this theory. With 

 one exception, however, all these remains have been found, 

 on more accurate and better conducted examination, to be, 

 instead of dissentient facts, beautiful proofs of its truth. The 

 exception to which we refer* is as yet, perhaps, unexplained, 

 and by some is considered as a stumbling block which must 

 cause the fall of this theory. If, however, we remember that 

 all the other exceptions have been explained, and that the 

 " Crocodiles'' teeth'''' of Burdiehouse, which Lyell considered 

 as indicative of the entire fallacy of this theory, have been 

 found by Professor Jameson, and afterwards by Agassiz, to 



" The occurrence of didelphic remains in the slate of Slonesfield, a 

 member of the oolitic series. 



