114 PICTURESQUE SKETCHES 



its close, we find that the fishes assumed their maxi- 

 mum of development, at least in the placoid and 

 ganoid orders, for at this time the reptilian fishes and 

 sharks were both numerous and powerful, while very 

 soon afterwards the whole tribe of fishes was repre- 

 sented by animals of smaller dimensions, of different 

 habit, and comparatively powerless. It is very in- 

 teresting in this case to watch the progress of the 

 transition. The fishes in the carboniferous rocks, 

 include many large shark-like and reptilian groups. 

 In the sandstone above the coal, and in the magnesian 

 limestone, are many nearly allied fishes, although of 

 much smaller size, but all the more advanced types 

 seem to fail. In the same newer beds, however, ap- 

 pear true reptiles, not indeed of large size, but of 

 complicated dentition, and the representatives of a 

 high group ; while, as we shall hereafter find, in the 

 beds of the secondary period the reptiles at first 

 exhibit high analogies and then pass off into a mag- 

 nificent series, including true representatives both of 

 the earlier sauroid fishes and the later aquatic mam- 

 mals. On the other hand, the fishes there exhibit a 

 lower form of higher groups, afterwards continued and 

 advanced to the most complicated types, but only 

 attaining a gigantic size in rocks of far newer date. 

 The bearing of these points on the general question 

 of development we shall have occasion afterwards to 

 allude to. 



