28 The American Naturalist. [January, 
ing edges of the continent, or in the impalpable sediment de- 
posited further away from the shore, or gathered in estuarine 
inlets, or they formed the denizens of purer and deeper waters 
and became later, in the secular changes of the earth’s crust, 
consolidated into limestone beds. This variation of position 
implied a greater or less likelihood of preservation as fossils. 
Darwin has observed that along the west coast of South 
America “ no record of several successive and peculiar marine 
faunas will probably be preserved to a distant age.” And the 
reason he assigns is that as the coast of that continent is rising, 
“the littoral and sub-littoral deposits are continually worn 
away, as soon as they are brought up by the slow and gradual 
rising of the land within the grinding action of the coast- 
waves.” The remains of animals so situated as to become ex- 
posed to the reassorting action and denudation of the shore 
currents and waves may suffer pulverization and dispersal, 
and those which are not soon covered by sediment may be 
dissolved or injured. Those farther away are entombed in 
the accumulation of sediment which falls down over the sea- 
floor more uninterruptedly at some distance from land where | 
it is less agitated and shifted by the waves and currents. In 
the elevation of the ocean bottom and its gradual change to 
dry land the emergent surfaces would undergo considerable 
disturbance from the waves, and along these eroded edges the 
fossils would disappear by crushing and attrition. Yet Dar- 
win’s observation seems scarcely so important, when we con- 
sider that the same stratum continued outward upon the slop- 
ing bed of the ocean is for some time exempt from this 
wearing, and during that time the sediments produced by the 
destruction of its own emergent portions are constantly ac- 
cumulating over it and rendering its own stability greater. 
This view has been indeed taken by Mr. Hopkins, who ex- — 
pressed his belief that sedimentary beds of considerable hori- — 
zontal extent have rarely been completely destroyed. Further- — 
more, we must remember that, in so far as we have indicated © 
three different cycles of deposition with their accompanying 
and characteristic forms of life, these animal forms are not re- 
stricted with any precision to these areas, and that organic 
