THE EHAETIC BONE BEDS 
223 
jaws, the softer parts swallowed, and the indigestible 
portions, such as scales, teeth, and broken bones, would 
be rejected and sink to the bottom. (The peculiar build 
of this Saurian, and the almost complete absence of such 
fragments in the coprolites, warrants the supposition that 
they were not swallowed.) On their way through the 
water these fragments were exposed to further attacks 
from the fishes, while any larger pieces which reached the 
lower depths were gone over by the big scavenger, Gera- 
todus, and still further broken up. The scene might be 
occasionally varied by a Saurian becoming a victim, and 
being served in a similar manner. The result would be 
a continual shower of these animal fragments to the sea 
bottom, and these, combined with coprolites, would form 
a deposit, the extent and thickness of which would be 
determined by two factors — (1) the size of the shoal ; (2) 
the time it remained at that station. 
After a time the shoal would shift to another locality, 
followed by the Saurians, and the same process would be 
repeated. But while the first Bone Bed was forming a 
considerable deposit of mud would settle elsewhere, and 
therefore the animal refuse at the second station would be 
deposited at a higher horizon than that of the first bed. 
Further shif tings of the shoal would occur at intervals, 
followed by deposits of “ Bone Beds,” each with an in- 
creased thickness of sediment beneath ; while the return 
of a shoal (or visit of another shoal) to a station previously 
occupied would account for the phenomenon of two or 
more Bone Beds in the same section. 
The patches or pockets occasionally met with might 
occur in two ways — (1) a comparative scarcity of the 
animals producing the deposit ; or (2) by their occurring 
while the shoal was moving from one station to another, 
when the resulting deposit would be both scanty and 
erratic in character. 
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