110 FISHES OF THE SILURIAN ROCKS, 



but it does not extend far. All the vertebrate remains yet 

 detected in the Silurian system, if we except the debris of 

 the Upper Ludlow bone-bed, might be sent through the Post- 

 Oftice in a box scarcely twice the size of a copy of the " Ves- 

 tiges." The naturalist of an exploring party, who, in cross- 

 ing some unknown lake, had looked down over the side of 

 his canoe, and seen a few fish gliding through the obscure 

 depths of the water, would be but indifferently qualified, from 

 what he had witnessed, to write a history of all its fish. Nor, 

 were the some six or eight individuals of which he had caught 

 a glimpse to be of small size, would it be legitimate for him 

 to infer that only small-sized fish lived in the lake ; though, 

 were there to be some two or three large ones among them, 

 he might safely affirm the contrary. Now, the evidence re- 

 garding the fishes of the Silurian formation very much resem- 

 bles what that of the naturalist would be, in the supposed 

 case, regarding the fishes of the unexplored lake ; with, how- 

 ever, this difference, that as the deposits of the ancient sys- 

 tem in which they occur have been examined for years in 

 various parts of the world, and all its characteristic organ- 

 isms, save the ichthyic ones, found in great abundance and 

 fine keeping, we may conclude that the fish of the period 

 were comparatively few. The palaeontologist, so far as the 

 question of number is involved, is in the circumstances, not 

 of the naturalist who has only once crossed the unknown lake, 

 but of the angler who, day after day, casts his line into some 

 inland sea abounding in shell-fish and Crustacea, and, after the 

 lapse of months, can scarce detect a nibble, and, after the 

 lapse of years, can reckon up all the fish which he has caught 

 as considerably under a score. The exi»t^ice of this great 

 division of the animal kingdom, like that of the earlier rep- 

 tiles during the Carboniferous period, did not form a promi- 

 nent characteristic of those ages of the earth's history in which 

 they began to be.] 



