
470 DYNAMICAL GEOLOGY. — [Boox III. 
sometimes replacing the calcareous parts of echini, molluscs, &c., 
while the surrounding matrix was, doubtless, still a soft watery ooze 
under the sea.’ , 
(3.) Phosphatic deposits, in the great majority of cases, betoken 
some of the vertebrate animals, seeing that phosphate of lime enters 
largely into the composition of their bones and occurs in their excre- 
ment (p. 169). The most typical modern accumulations of this nature 
are the guano beds of rainless islands off the western coasts of South 
‘America and Southern Africa. In these regions immense flocks of 

Fig. 181.—RapioLarian Ooze. 
Dredged up by the Challenger expedition, from a depth of 4475 fathoms, in Lat. 11° 
24’ N., Long. 143° 10' FE, Magnified 100 diameters. This is from the deepest 
abyss whence organisms have yet been obtained. 
sea-fowl have, in the course of centuries, covered the ground with an 
accumulation of their droppings toa depth of sometimes 80 to 80 feet, 
or even more. ‘This deposit, consisting chiefly of organic matter and 
ammoniacal salts, with about 20 per cent. of phosphate of lime, has 
acquired a high value as a manure, and is being rapidly cleared off. 
It could only have been preserved in a rainless or almost rainless 
climate. In the west of Europe isolated stacks and rocky islands 
in the sea are often seen to be white from the droppings of clouds 
of sea-birds; but it is merely a thin crust, which is not allowed to 
grow thicker in a climate where rains are frequent and heavy. 
' See Wallace, Q. J. Geol. Soc, xxxvi., Sollas, Ann. & Mag. Nat. Hist. 5th series, vi. 
p- 487, aud ante, p. 463, ; 
