102 PICTURESQUE SKETCHES 



way to the advance of other and higher groups. In- 

 numerable sharks of all sizes, and perhaps of many 

 forms, rapid and powerful swimmers, fiercely and insa- 

 tiably carnivorous, were associated with huge mon- 

 strous fishes, more resembling reptiles than any of 

 their own class at the present day, and incredibly 

 powerful and voracious. The fishes at this time had 

 attained, it would seem, their maximum of develop- 

 ment in point of vigour, and in some respects (though 

 in some respects only, and by analogy) in struc- 

 ture ; and it is not a little interesting to find, that, 

 at this point, so far as we can tell, the true rep- 

 tiles were actually introduced (the remains of that 

 class being indicated in the coal-measures, and ac- 

 tually found in the magnesian limestone associated 

 with carboniferous species of fishes). 



The reptiles thus appearing were not, however, 

 members of that group through which the passage 

 from sauroid fishes to true saurians takes place, but 

 belonged to a higher form, and to a complicated type 

 of that form. It seems clear, therefore, that, while 

 progression and a general advance in point of organiza- 

 tion is in one sense a method observed by nature, 

 still there is not such a regular gradation that an 

 animal of lower organization can be supposed to be 

 employed as the agent in introducing a higher group ; 

 this view, however plausible, not being borne out by 

 observation, but, on the other hand, being distinctly 

 contradicted by the results of geological and palseon- 

 tological investigation. 



