236 ANNUAL OF SCIENTIFIC DISCOVERY. 



of this shore could have been at the time of the deposition of the 

 phosphates so different from what it is at present, as would have 

 been required to produce the dry conditions essential to the accu- 

 mulation of a guano deposit. 



" There is another view of the origin of these phosphate beds, 

 which, so far as my knowledge goes, has not yet been suggested, 

 and which, it seems to me, solves a part of the difficulties. 



" The phosphate layer rests upon a mass of marl containing a 

 number of fossils which are found in a worn condition mingled 

 with the phosphate nodules. The analyses of Dr. St. Julien 

 Raven el have shown that at several points beneath the phosphate 

 beds the marl contains several per cent, of phosphate of lime, and 

 it may be assumed as eminently probable that the whole of .the 

 marl beneath the region where the phosphate beds occur contains 

 a certain quantity of this material, mingled with the carbonate of 

 lime which constitutes the mass. Now it is a well-known fact 

 that water containing carbonic-acid gas in solution has a solvent 

 action upon both these salts of lime, but that its power is greatest 

 on the carbonate of lime. So that a mass of marl containing both 

 these materials, submitted to the action of water charged with 

 carbonic acid, might have the carbonate of lime entirely removed, 

 and the mass left behind when the solvent action ceased might 

 consist almost altogether of the phosphate of lime. 



" If we look a moment at the conditions which prevail in the 

 phosphate region, we shall see that with this view we can easily 

 frame an explanation of the formation of this phosphate layer. 

 The usual section through these beds gives us on top a layer of 

 vegetable matter and soil containing humus, through which the 

 water percolating becomes charged with carbonic acid ; then the 

 phosphate layer; immediately beneath that the marl containing 

 phosphates, which is only slightly permeable to water. Soaking 

 over this marl the water becomes charged with carbonate of lime 

 and some phosphate, which it carries away in the drainage system 

 of the country. This process, going on for centuries, gradually 

 dissolves away a great thickness of the marl, and gives, as in the 

 capping bed, an accumulation made up of fossils from the wasted 

 beds, which resisted decay, and could not be washed away ; of 

 phosphates which became aggregated into nodules; of remains 

 of man and other recent animals, which, falling in the swamp, 

 sank through the soft bog and became trampled in among the 

 nodules by the living animals which inhabited this low land. 



" Great freshets might lay down several feet of clay and sand 

 or some rearranged marl on top of the phosphate layer, thus con- 

 fusing the record, by making the remains of man and extinct 

 animals associated with his early history in this region seem a 

 part of the ancient marl beds. 



'-'Looking upon the phosphate layer as the debris of a large 

 amount of eroded marl, it is no longer a difficult matter to account 

 for the association of fossils found there, which would be inexpli- 

 cable without some theory of this kind." 



As to the manner of accounting for the presence of phosphoric 

 acid in the marls in such quantity and so regularly disseminated, 



