640 



THE WONDERS OF GEOLOGY. Lect. VI. 



others by siliceous infiltrations.* Large masses of a. cel- 

 lular coral (Eunomia radiata) abound in the limestones 

 of the Great Oolite. The corals, shells, &c. are for the 

 most part of extinct species and genera. Those who have 

 visited districts where the Coral-rag forms the immediate 

 sub-soil, and is exposed to view in the quarries, or in 

 natural sections, must have been struck with the resem- 

 blance of these rocks to modern coral-banks. We know 

 that in our present seas all situations and circumstances 

 are not alike favourable to the existence and growth of 

 polyparia ; in some parts of the ocean they abound, and in 

 others are altogether wanting. In like manner in the 

 deposits of the Jurassic formation, which extend over a 

 great part of Europe, and have been formed in a sea of 

 vast extent, beds of coral are not universally distributed, 

 but occur only in certain districts ; in other words, they 

 occupy the situations which in their native seas presented 

 the conditions required by their peculiar organization. 



The Lias contains comparatively but few polyparia ; and 

 the Trias only a small number, including three or four 

 species of Gorgonia, three of Retepora, and one of Astraea. 



35. Corals of the Palaeozoic Formations. — The 

 Mountain limestone of the carboniferous system, which 

 will come under our notice in the next discourse, abounds 

 in the cellular, and lamelliferous zoophytes : and many of 

 the deposits of the Devonian and Silurian systems, teem 

 with anthozoan corals ; for the most part of peculiar forms, 

 and typical of particular groups of strata. The corals of 

 the Silurian deposits of England, f equally prevail in the 

 corresponding strata of North America. J 



* In the chert of the Portland oolite of Tisbury, Wiltshire, masses 

 of a beautiful silicified coral occur ; a fragment of a polished section 

 is shown in Lign. 141, fig. 9. 



f Sir E. I. Murchison's * Silurian System," vol. ii. 



X See Professor Hitchcock's " Geology of Massachusetts," and Pro- 

 fessor Hall's " Gcoloffv of the State of New York." 



