GEOLOGY: E. BLACKWELDER 
493 
At somewhat rare intervals, marine animals are killed in enormous 
numbers by sudden changes in temperature, by volcanic eruptions, 
submarine earthquakes, and other catastrophes. The carcasses of such 
animals generally float; but some may come to rest upon the sea bot- 
tom. In either event the omnipresent forces of decay rapidly convert 
the carcasses to soluble form and thus return their constituents to the 
oceanic solution before they are deeply buried. It is conceivable that, 
under the most favorable circumstances, a layer of bones and teeth 
might be left on the sea floor; but at best the reality of fixation in this 
manner is doubtful. 
As an incident to the normal life of vast numbers of organisms both 
on the sea bottom and in its upper waters, shells and pellets of solid 
excrement are incessantly falling to the sea bottom. Dredging opera- 
tions have shown that in many places the latter material forms an ap- 
preciable part of the bottom sediments^ and in a fev/ places the sediment 
has been found to consist almost entirely of such pellets, especially those 
of holothurians, marine worms, and echinoids. Under normal condi- 
tions, this material is devoured by the various scavengers of the sea 
bottom, and any portion that may be left is fermented by bacteria. 
Insofar as this action prevails, phosphorus cannot well become a solid 
part of the sediment deposited on the sea floor. 
Under conditions probably anaerobic but not yet well understood, a 
quite different process may operate. The organic refuse fermented by 
bacteria in the absence of free oxygen yields such compounds as hydro- 
carbons, carbon dioxide, hydrogen sulphide and ammonia. Under favor- 
able chemical conditions the phosphoric acid also liberated will react 
with various substances, particularly lime salts. With the latter it 
produces the mineral collophanite, a hydrous calcium carbo-phosphate.^ 
Where calcareous shells lie on the sea bottom, they become phospha- 
tized. Even organic matter such as excretory pellets, pieces of wood, and 
other non-calcareous materials, are altered in this way. Bones which 
initially contained about 58% calcium phosphate are still further phos- 
phatized until that percentage rises to 85 or more. In addition, the 
collophanite forms little round grains resembling the oolitic grains 
common in certain limestones. It is also deposited as a cement be- 
tween the particles of all kinds, thus producing hard nodules or even 
continuous solid beds of phosphate rock. At the same time, probably 
by the influence of carbonic acid evolved during the decay of the organic 
matter, Hme carbonate is dissolved. Many facts indicate that in these 
situations only the phosphatic mineral is stable, even though lime 
