22 



DISTRIBUTION OF ORGANIC REMAINS 



many of the strata appear to be composed almost entirely of their 

 mineralised exuviae, but generally in a broken state. The chain co- 

 ral occurs occasionally in transition limestone. Other genera of ra- 

 diated animals occur in the more recent formations of limestone, but 

 seldom in sufficient abundance to compose nearly the whole mass of 

 a stratum. This is the more remarkable, as coralline animals are 

 forming extensive calcareous rocks in our present seas. Some gen- 

 era and species of radiated animals which abound in transition rocks, 

 have not left their remains in any of the upper strata ; hence it might 

 be inferred that they had long been extinct. In some instances, the 

 inference is not correct; the Madrepora stylina, so common in tran- 

 sition lime-stone, is entirely wanting in the secondary and tertiary 

 strata ; but a living animal of this species has been recently discover- 

 ed in the South Seas. The pentacrinus, which is distinguished from 

 the encrinus chiefly by its pentagonal stem and branches, makes its 

 first distinct appearance in the lias, but is not frequently met with in 

 the upper strata, and disappears entirely in the uppermost forma- 

 tions : hence it was long supposed that the species was extinct. A 

 living pentacrinus has, lately, been discovered in the West Indies, 

 and its stem and branches in a perfect state have been sent to this 

 country ; and, still more recently, a living pentacrinus was found in 

 the Cove of Cork. 



The genus echinus makes its first appearance in the midst of the 

 secondary strata, and various species are continued into the cKalk, 

 which abounds with remains of this animal, in high preservation. It 

 may be remarked, that scarcely any calcareous stratum, abounding 

 in marine organic remains, has been examined, in which remains of 

 some species of radiated animals may not be found. 



Articulated Animals. — Some species of vvorms (annelides) inhab- 

 iting tubes, have left their remains in the upper secondary, and ter- 

 tiary strata : remains of crustaceous animals (crabs, &;c.), are not nu- 

 merous in the upper secondary strata, where they first occur ; but 

 they are more common in chalk and the tertiary beds of clay cover- 

 ing chalL One of the very first inhabitants of the globe appears to 

 have been a crustaceous aquatic animal, called in England the Dud- 

 ley fossil, from its being first noticed in the transition limestone near 

 that town. Its more appropriate name is the Trilobite, from the 

 three parallel lobes or divisions of the body, with ranges of transverse 

 ventral fins, somewhat similar to those under the tail of a lobster. 

 The largest species are found in the slate quarries at Angers, in 

 France. A specimen in my possession, from that place, measures 

 seven inches in length : the body has taken the flat form, common 

 to almost all fossils found in slate, (See Plate 5.) it scarcely rises 

 more than one third of an inch above the surface of the slate ; the 

 upper slate contains the impression or mould of the animal. To this 

 species Guettard has given the name of Ogyges, from its occurrence 

 among the most ancient rock formations, that contain vestiges of or- 

 ganic life. 



