172 PICTURESQUE SKETCHES 



regard to such parts as the cartilaginous fins of the 

 paddle, and the position and shape of the tail, or 

 rather tail-fin, the reader will naturally conclude that 

 the subject is exhausted, and that it remains only to 

 sum up into a general view these various details. But 

 the case is not so. We have seen that in this bed'of 

 fine mud, the bodies of animals were deposited and 

 preserved so completely, that the skeletons, after the 

 soft parts had decayed, retained their relative position, 

 exhibiting all the important points of structure. Cir- 

 cumstances, however, sometimes occurred by which 

 individuals, overtaken perhaps by sudden destruction, 

 have been at once embedded, a perfect cast being 

 formed of every part, internal as well as external, so 

 that the skin, the contents of the stomach, its propor- 

 tional magnitude and other details, may be learnt 

 by careful study of the specimens thus embalmed and 

 handed down to us. But, before dwelling upon these 

 obscure and minute points, there are others to be men- 

 tioned scarcely less curious, resulting from the conti- 

 nued resort of great families of these monsters to par- 

 ticular spots. Possibly these spots may have been 

 good feeding-ground, and favourable for the deve- 

 lopment of the larger mollusca and fishes, or the pre- 

 sence of shallows and neighbouring land may have 

 been especially advantageous for breeding; but, at 

 any rate, it is certain that we find, here and there, 

 localities where vast multitudes of pellets of an oval 

 shape and various size are accumulated. These pellets 

 often contain fragments of bone, teeth, or fish scales, 

 and are now recognized as being beyond question the 

 fossilized dung of the great marine reptiles. They 

 are spoken of by Geologists under the name of Co- 



