THE GEOLOGIST 
shell-fish from their oosy homes, and note their positions in the earth ; 
observe the zones of various plants and living thuigs, and how they 
vary with the depth of tide or the kind of soil or sea-bed, and carry 
back your experiences to the quarry, and then you will perceive 
something, and as yet something only, of the value of a fossil. 
On our shores are three zones, of materials, animality, and 
vegetation. The sea has sorted out the sand and mud from the 
heavier fragments, — which the restless waves have tossed along the 
strand and have rounded into boulders and pebbles, — and, between 
the tidal marks, has left the sand, while the finer particles have 
been carried into the region of, and below, low water. 
So too, nature presents her three zones of animal and vegetable 
life ; and, as the briny currents have carried the still finer particles 
of silt into yet lower depths and more profound abysses, so nature 
in the deeper waters presents other zones of created beings, with 
characters and habits equaUy suited to the varied conditions of their 
existence. The reseaiches of modem naturalists have shown that 
not only are various forms of animals and vegetables circumscribed 
in their geographical distribution, but that they are also limited in 
their vertical range, or in other words, are prescribed within a 
certain depth of the sea, or a definite elevation of the land. Most 
organic remains, from the very means and circumstances of their 
preservation, are necessarily of marine origin, because terrestial 
or subaerial influences are more essentially destructive in their 
ordinary action ; and it is more rarely in comparison to the sub- 
marine operations, which are constantly at work, that those co-inci- 
dences happen by which the relics of the land, or even of the 
river or lake, are preserved. 
Of actual depths of seas, the shell-fish or MoUusca, from the 
limited range of their locomotive powers, must be, next to algae, 
corals, bryozoa, and other Jixed forms, the most certain and definite 
in the evidence they afford ; and thus it will be perceived, what an 
important bearing the study and knowledge of tlieir habits, 
regions, and ordinaiy Umits of depths will have in determming from 
the fossil species through their relations to their recent types, the 
conditions under which the strata, in which they are embalmed, 
were deposited, and the profundity of the pre-adamic seas or 
estuaries. As by the modifications and adaptations which are pro- 
