Dec, 1886.] elliott society. 129 



charged with the sweepings from guano beds, formed above them by the con- 

 gregation there, at some indefinite time in the past, of vast flocks of birds. 



A second theory, which was advanced by Prof. F. S. Holmes, maintains that, 

 at a remote geological period, before the extension of the coast line to its pres- 

 ent Hmits, there existed lagoons of salt' water at some little distance from the 

 ocean, which were visited by vast herds of animals from the interior country, 

 such as the mastodon, elephant, bison, etc., just as animals assemble now about 

 the salt-licks of Kentucky, to obtain the salt which is essential to their exist- 

 ence, and that, in this way, the nodules, which had been left upon the reces- 

 sion of the sea, became charged with the phosphoric acid contained in their 

 excrements and remains. 



A third explanation of the formation of these rocks is that "certain mol- 

 lusks possess the power of separating the phosphate of lime from sea water, and 

 that, through theii- instrumentality, the marl, and especially the upper strata, 

 became charged with a certain amount of phosphate of lime. That the pro- 

 portion of the phosphate of lime thus obtained to the whole body of the super- 

 ficial layers of the marl was afterwards increased. 1st, By the removal of a 

 considerable amount of the carbonate of lime, rendered soluble by the percola- 

 tion through it of rain water containing carbonic acid, derived from the de- 

 composing vegetable matters in the soil overlying the marl. 2d, By a well 

 known proneness of phosphoric acid, when diffusely distributed, to concentrate 

 and to give rise to concretionary processes, similar to those observed in the 

 fl."nt nodules and pebbles of the English chalk. This theorj" agrees with the 

 diffused occurrence of phosphate of lime in the superficial layers of the marl, 

 as well as with the fact that the upper layers of the deposits and the outside of 

 the nodules are the richest in phosphate. It substitutes for a local cause a 

 general one, commensurate at once with the wide area occupied by the phos- 

 phate rocks, and by the phosphatic marls of the South Atlantic seaboard. 

 Such a cause might have been in operation ages ago, when the layers of phos- 

 phate rock, found at a depth of 300 ft. in artesian borings, were formuig : 

 and it may be in operation now, as the dredging work of the United States 

 Coast Survey shows that the marls accumulated at the depth of 200 fathoms, on 

 the floor of the Gulf Stream, between Florida and Cuba, contain a considerable 

 percentage of phosphate of lime. " * 



There is plausibility in each of these theories, and it is not the pui-pose of 

 the writer to attempt to disprove them. His object in this paper is to advance 

 another theory which he thinks is entitled to consideration. 



It is, that the phosphorus contained in the phosphate rock was derived from 

 the decomposing bodies of a great number of immense sharks, whose extinction 

 was sudden and general, and due to the cold of the glacial period. 



It must be explained here that the phosphate rock in question is of two 

 kinds, — the land and the river rock. The first is found at a depth of from 2 to 

 10 feet below the surface of the soil, and is usually in masses or nodules, vary- 



* Resom-ces and Population of Soutli Carolina, by Agricultural Department of the 

 State, 1SS3, page 49. 



VOL. n. 17 riiblisliedMay,lSS7. 



