GEOLOGY. 215 



taken up. Before the Glasgow Philosophical Society, reported in 

 Chemical News. 



Formation of Limestone. The littoral and deep-sea dredgings, 

 undertaken by the United States Coast Survey in the Gulf Stream 

 in the vicinity of Florida, have contributed much information, not 

 only with regard to the fauna of the ocean at various depths, but 

 also with regard to the geological history of the past. In speak- 

 ing of the formation of limestone, now going on near the Florida 

 coast, Professor Agassiz (in his report quoted above) says : 

 " We find upon the Florida reefs, as well as between the innumer- 

 able keys stretching along the American coast, and upon the 

 coral plateau sloping towards the main trough of the Gulf Stream, 

 extensive beds of regularly stratified rocks of various kinds." 

 One area in particular, beginning at a depth of about 50 fathoms 

 and extending to a depth of about 250 fathoms, constitutes a 

 broad slanting table-land. The floor is rocky; " it is, in fact, a 

 limestone conglomerate, a kind of lumachella, composed entirely 

 of the solid remains of organized beings, a true concretionary 

 limestone, such as we might find in several levels of the Jurassic 

 formation and more especially in that horizon which geologists 

 call Coral Rag. Large fragments of this rock were brought up 

 by the dredge ; so that its structure and characteristic remains of 

 animals could be studied at leisure. I do not know that there is 

 on record in the annals of our science a more direct illustration of 

 the manner in which mountain-masses of calcareous deposits 

 have been accumulated on the bottom of the ocean. Such a for- 

 mation exists nowhere else within the range of the Gulf Stream, 

 unless it should be hereafter ascertained that a similar deposit 

 extends along the submarine border of our continent, edging the 

 American wall of the deeper part of the Atlantic trough. But in 

 the shoal waters intervening between the coast of the peninsula 

 of Florida and the keys and reefs, there exist various deposits of 

 an entirely different structure, the accumulation and increase of 

 which are constantly going on. The most extensive of these 

 formations is a regularly stratified oolitic rock, the grains of which 

 vary from imperceptible granules to larger and larger oolites, 

 approaching the dimensions of pisolites, and cemented together 

 by an amorphous mass of limestone mud. The oolites themselves 

 are formed in the manner first described by Leopold von Buch. 

 Hard particles of the most heterogeneous materials, reduced to 

 the smallest dimensions and tossed to and fro in water charged 

 with lime, are gradually coated with a thin film of limestone, and 

 then another and another, until they sink to the bottom to be further 

 rolled up and down the sloping shore bottom until they_become 

 cemented with other similar grains, and form part of the grow- 

 ing limestone bed. Of course, the finer oolites are seen nearest 

 the shore line, and it is instructive to see at low tide the little 

 ripples of successive larger oolites left dry as the water subsides. 

 Naturally these materials are frequently thrown up along the 

 beaches in layers of varying thickness, and in course of time 

 become cemented, and are transformed into solid rock, over 

 which crusts of hard, compact limestone are in the end formed 



