176 PICTURESQUE SKETCHES 



animals, proving that they had floated or been drifted 

 far out to sea. The change in the sea-bottom, and the 

 lapse of time, accompanied by the upheaval or sink- 

 ing of land, produced the effect of destroying many 

 old species, while other new ones entered the field. 

 These exhibited an undoubted approximation to the 

 animals of a later period, and include some very 

 curious star -fishes, several crustaceans, and a large 

 number of mollusca or shell-fish, both bivalve and uni- 

 valve, all having analogies with existing species, though 

 all specifically different. Of these the most remark- 

 able in their departure from the existing type are 

 the Pentacrinite, the Terebratulse among bivalve shells, 

 and the ammonite and belemnite among the univalves. 

 The fishes and the reptiles exhibit still more promi- 

 nently the differences that then existed. 



If we wish to pass in review the various groups 

 most characteristic of this singular period, concerning 

 whose natural history we have so many and such dis- 

 tinct facts recorded, we must imagine a wide tract 

 of open sea, into which a quantity of fine sediment 

 of calcareous mud was in some way carried and depo- 

 sited."" 5 ' From the distant land whence this mud was 

 washed came also occasionally trunks of trees con- 

 veyed by marine or river currents. Attached to them, 

 and also occasionally fastened to sea-weeds or other 

 floating bodies, would appear in large clusters (like 

 the bunches of barnacles sometimes suspended from a 

 ship's bottom) the singular pentacrinites, their long 

 stony column fringed thickly with branches of articu- 

 lated stone, with a stony coat of mail surrounding the 



* Such a deposit is probably now going on in the Yellow Sea, off the 

 coasts of China. 



