466 GEOLOGICAL DISTRIBUTION OF ECHINODERMATA. 



Marble. " The substance of this marble," says Dr. Buckland, 

 " is often almost as entirely made up of the petrified bones of 

 Encrinites, as a corn-rick is composed of straws. Man applies 

 it to construct his palace, and adorn his sepulchre ; but there are 

 few who know, and fewer still who duly appreciate, the sur- 

 prising fact, that much of this marble is composed of the skeletons 

 of millions of organised beings, once endowed with life and sus- 

 ceptible of enjoyment, which, after performing the part that was 

 for a while assigned to them in living nature, have contributed 

 their remains towards the composition of the mountain masses 

 of the earth." It cannot be deemed improbable that, of those 

 forests of Encrini to which these depositions are principally 

 owing, some grew on the sides of the Coral reefs from which 

 other beds of limestone seem to have originated ; and that the 

 debris (or separate particles) of the reefs furnished the calcareous 

 matter, by which their skeletons are held together. Fragments 

 of Encrinites are also dispersed irregularly throughout all the 

 deposits of the Transition period, intermixed with the remains 

 of other contemporary marine animals. No other species of 

 Echinodermata, however, as yet present themselves ; and it is 

 interesting to remark, that the Crino'idea which so abound in 

 the Transition epoch (more than thirty species being known) 

 belonged, with one exception, to the Encrinus and other round- 

 stemmed genera, and were therefore more unlike the existing 

 forms of that family, than were those which we find at a later 

 period. All these Crino'idea, which continue to abound in the 

 Mountain Limestone and other of the more ancient secondary 

 rocks, become extinct when we arrive at the Lias ; and are then 

 replaced by the Pentacrinus. The stems of Encrinites compose 

 extensive beds in the Carboniferous, as in the Transition series ; 

 and these are often found in the neighbourhood of those of a 

 distinctly Coralline nature, so that the animals probably grew 

 on the banks of such reefs as are now being elevated in the 

 Southern Ocean, and which, if properly examined, might be 

 found to support their living analogues. The joints of the 

 Encrinite-stems often fall asunder when the connecting rock is 

 not firm enough to hold them, the animal membrane which 



