14 GENERAL ACCOUNT OF THE DEPOSITS. 



Post Pliocene age in which masses of more coherent rock, rich in 

 calcium phosphate are intermingled. The masses are of irregular 

 shape and of all sizes, "from pebbles up to 1000 pounds and more" 

 (Leidy), and they are much tunnelled by Lithophagi. Now these 

 masses, except for their phosphatic elements, are similar to the rock 

 of the underlying Eocene and Miocene formations and contain the 

 same fossils. Concerning their origin Prof. Leidy writes "at this 

 time [when the older Eocene and Miocene Marls were being broken 

 up] or later, neighbouring and superficial islets, the resort of 

 myriads of sea fowl, may have furnished the material which when 

 washed with the ocean and mingled together with the decomposing 

 remains of marine animals, supplied the elements for the conversion 

 of the porous rock marl into the more valuable phosphatic com- 

 pound." Such was the explanation originally offered by Mr 

 Holmes, and suggested, it seems to me, long ago by MM. Way 1 , 

 and Paine who also considered the phosphates to be of organic 

 origin. As a result of their chemical researches these gentlemen 

 write, — "That the phosphate of lime has penetrated the various 

 fossils and nodules from without there scarcely exists the smallest 

 doubt." 



Some actual cases of such an addition of phosphatic material 

 to calcareous rocks in very modern times have been described by 

 Prof. Dana 2 as occurring in fragments of coral rock included in 

 guano at Howland's Island in the Pacific ocean; and another 

 interesting example observed in Cave Ha near Giggleswick, was 

 recorded by Mr J. E. Marr of St John's College in the Geological 

 Magazine for 1876, p. 268. From this account it appears that 

 some stalagmitic layers of carbonate of lime have become phos- 

 phatised by the percolation through them of water which had 

 passed through an overlying organic deposit, made up for the most 

 part of the bones of small mammals and birds (from the pellets 

 of owls, etc.). "The only apparent way," writes Mr Marr, "in 

 which it seems that the travertine could have become phosphatised, 

 is by the percolation of water through the pellet bed, until it was 



1 " On the Phosphoric Strata of the Chalk Formation," by J. M. Paine and 

 J. T. Way. — Journal Royal Agricultural Society, 1 Ser. Vol. ix. pp. 56 — 84. 



Mr Godwin Austen believed, 1848, that the phosphatic matter was of coprolite 

 origin. — Quar. Jour. Geol. Soc. Vol. iv. p. 257. 



2 Corals and Coral Islands, p. 283. 



