TIE 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 formations 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 medixval 
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 
small 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,G00 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 floarished the Belemnites (Thun- 
derstones), supposed by the ancients to be 
Ammonites, or Snake-Stones, 
Belemnites. 
the thunderbolts of Jove, but now known «@ B acutus. 
6. Belumnite (restored). 
to be the petrified internal bones of a race of 
voracious ten-armed cuttle-fishes, whose importance in the 
GG2 
