74 REVIEWS. 



coral reefs, and even there only in particular situations favourable to 

 their formation." 



" The extensive system, denominated the Muschel-Kalk, is singularly 

 characterized by the scarcity of its corals ; in no portion of it is there 

 any unequivocal evidence of the existence of coral reefs. This formation 

 seems to have been a purely sedimentary deposit, the organic fossils of 

 which belong chiefly to the class Mollusca, as the name itself (shell lime- 

 stone) indicates." 



" The coral banks of the Jura are developed in inverse proportion to this 

 last. No other formation affords such decisive evidence of the effective 

 part which the coral animals have taken in the formation of the upper 

 strata of the globe. The members of this group, in their protracted 

 parallel layers and defined terraces, exhibit, in unaltered position, walls of 

 rock built up entirely of coral, and, at the foot of these, huge masses of 

 coral debris which have been cemented by finely comminuted particles of 

 lime, telling of the raging surf that broke against those reefs in days of 

 old. These fragments are intermixed with other fossil remains varying 

 with the localities, and form united a motley conglomerate, which is known 

 under various names, but most commonly as Coral Breccia. Generally, 

 the coral reefs of the Jura have more the character of Barrier reefs, and 

 they seem to have extended parallel to the coast at a moderate distance 

 from it, as exemplified in the coral reef of New Caledonia. Such a reef 

 extended, during the Jurassic period, right through the south of Germany 

 and the west of Switzerland, from the neighbourhood of Geneva away to 

 Ratisbon, and thence northwards to the river Main, between Bamberg and 

 Baireuth." 



"Not less extended was the system of coral reefs in the succeeding 

 Cretacean period, the greatest part of the chalk being derived from corals, 

 at least as a deposit. In the chalk period there existed already large 

 land-locked seas, such as the Red Sea at present ; and on the shores of 

 these the coral animalcules wrought in undisturbed tranquillity, and in 

 concert with innumerable Polythalamia, deposited the whole mass of the 

 white chalk, which is more than five hundred feet in thickness. The 

 effective part which the Polythalamia have had, ever since, in the formation 

 of the calcareous rocks, shows that flat tracts of coast have prevailed exten- 

 sively. We have compared the terraces of the Jura to Barrier reefs, in 

 the chalk we find more resemblance to the Lagoon reefs (" Atolls") ; 

 although the chalk basins were not, strictly speaking, Lagoon islands, but 



