THK BELEMNITES. 



437 



these remarkable crustaceans, yet but few of their petrified 

 remains, so numerous in the Silurian and Devonian strata, are 

 found in the carboniferous or mountain limestone, and none 

 whatever in formatious of more recent date. Thus, long before 

 the wind ever moaned through the dense fronds of the tree ferns 

 and calamites which once covered the swampy lowlands of our 

 isle, and long before that rich vegetation began, to which we are 

 indebted for our inexhaustible coal-fields, now frequently buried 

 thousands of feet below the surface on which they originally 

 grew, the Trilobites belonged already to the things of the past ! 



In the seas of the mesozoic or mediaeval 

 period, new forms of life appear upon 

 the scene. A remarkable change has 

 taken place in the cephalopods ; for the 

 chambered and straightened Orthocera- 

 tites and many other families of the 

 -order have passed away, and the spiral 

 Ammonites, branching out into nume- 

 rous genera, and more than 600 species, 

 now flourish in the seas, so that in some 

 places the rocks seem, as it were, com- 

 posed of them alone. Some are of 

 email dimensions, others upwards of 

 three feet in diameter. They are met 

 with in the Alps, and have been found 

 in the Himalaya Mountains, at elevations of 16,000 feet, as 

 eloquent witnesses of the vast revolutions of which our earth 

 has been the scene. Carnivorous, and re- 

 sembling in habits the Nautili, their small 

 and feeble representatives of the present day, 

 their immense multiplication proves how nu- 

 merous must have been the molluscs, crusta- 

 ceans, and annelides, on which they fed, all 

 like them widely different from those of the 

 present day. 



Then also flourished the Belemnites (Thun- 

 ■derstones), supposed by the ancients to be 

 the thunderbolts of Jove, but now known 

 to be the petrified internal bones of a race of 

 voracious ten-armed cuttle-fishes, whose importance in the 



G o 2 



Ammonites, or Snake-Stones. 



Belemnites. 

 a. 6. acutus. 

 6. Eelemnite (restored). 



