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and pointed out the difference between those which have no 

 calcareous skeleton, like the " Sea Anemone," and those which 

 build coral structures or reefs in tropical seas ; the calcareous 

 material of which they are constructed being derived from the 

 water of the ocean, and by colonies of these tiny architects 

 working in unison, structures of gigantic proportions are pro- 

 duced. The lecturer then shewed how the reef-building corals 

 can only live and work in water having a temperature of from 

 80° to 82°, and as that condition is now chiefly found between 

 30° north and south of the equator, their operations are for 

 the most part confined within those Hmits ; while even in those 

 latitudes, where the ocean is traversed by cold currents, their 

 Zoophytic life is absent. He then explained that in certain 

 areas of the earth's surface some portions are subsiding while 

 others are rising ; that observation had shewn that the Coral 

 sea of our time is a vast area of depression, and that the life- 

 conditions within that area being very favorable to the develop- 

 ment of the Polyp, there was a prodigious growth of reef- 

 secretion ; that when they built around land, it formed a 

 " fringing reef ; " when that land underwent a further subsi- 

 dence, it became a "barrier reef;" and that when the land 

 became entirely submerged, rings of coral, like Wliit- Sunday 

 Island, alone remained to attest the former presence of terra 

 firma. He then explained how the waste of the reef is ground 

 into a fine mud or coralline sand, that the calcareous paste coats 

 particles of sand which become cemented around the nucleus, 

 and how, by the constant roll and agitation of an ever restless 

 sea, these physical conditions lead to the production of oolitic 

 limestones, which are found around the shores of coral islands 

 of our own time. Having thus established the fact that oolitic 

 limestones are produced under the conditions just described, he 

 proceeded to apply this natural history fact to an explanation 

 of what had not hitherto been attempted, namely, the genesis 

 of the oolitic rocks, some of which they had that day seen. He 

 said that the oolitic series of rocks may be described generally 

 as a succession of argillaceous deposits, as the Lias, Oxford 

 Clay, and Kimmeridge Clay, with interposed beds of oolitic 



