536 ANCIENT CORAL- FORMATIONS. 



trace very distinctly the mode in which three principal kinds of 

 limestone rocks may have taken their origin from Coral 

 formations. 



1109. Now, the Mountain, or Carboniferous Limestone, a 

 rock very abundant in Britain, extending over large areas 

 beneath the coal-fields, and sometimes exhibiting a thickness of 

 nearly 3000 feet, though in some parts evidently composed 

 of accumulations of Shells, Encrinite stems, &c., exhibits the Coral 

 structure very distinctly in many situations ; and these parts are 

 so blended with the neighbouring rock, as to make it appear 

 probable that the latter also was once in the state of coral, but 

 was gradually changed by the process just described. Further, 

 the collections of other animal remains are such, as we should 

 expect to find on the margin of a coral reef or island existing at 

 that epoch ; and a similar process of fossilization is taking place 

 at this very time, on the shores of the islands now being built up, 

 the species of animals imbedded being, however, not the same. The 

 great thickness of the beds of this rock may be very well accounted 

 for, in the same manner as the depth of the coralline masses of 

 recent formation ( 1077)- The Oolite had its origin in the 

 wearing-down of the older limestone beds, with additional matter 

 derived from the skeletons of the races of animals, which existed 

 during the period of its formation. And there can be little doubt 

 that the C7*#/&-formation owes a considerable part of its substance 

 to the same sources ; though part was doubtless derived from the 

 decomposition of shells, and a large proportion in some situations 

 from the remains of animals of extreme minuteness, presently to 

 be described ( 1107). There are observed, in rocks of more 

 recent formation, appearances which still more clearly indicate, 

 that they too were originally formed by Coral-polypes. These 

 are often found within narrow limits, as if they had been reefs 

 or islands of small size. Thus we find a stone, called Coral- 

 rag, in Oxfordshire ; and very distinct Coral- beds in the Crag 

 of the eastern coast of England. It is interesting to remark, 

 that the remains of Coral, which are found in the older limestones, 

 all correspond with those at present abounding near the equator, 

 and exhibit the Lamelliform structure ( 1069) ; whilst they are 



