502 A POPULAR EXPOSITION OF THE 
With regard to the first condition, it is abundantly evident that 
aquatic types are far more favourably circumstanced for preservation, 
than purely terrestrial forms; and littoral species, again, more so 
than pelagic tribes. But, allowing the body of the dead fish or float- 
ing cephalopod to be cast, uninjured, by winds and currents, on the 
shore, or the drowned mammal swept down to the river estuary, the 
co-operation of various conditions is required to ensure its presérva- 
tion. Briefly—there may be no sediments under process of distribu- 
tion at the spot; or the sediments may not be thrown down with 
sufficient rapidity to arrest decomposition ; or the shore may be rocky 
and exposed, and mechanical destruction follow. Finally, if en- 
tombed forthwith, its calcareous parts may be dissolved out to 
constitute a cementing material for the surrounding mass; or subse- 
quent metamorphic agencies may obliterate all traces of its form. 
The more an organised substance approaches inorganic matter in its 
composition, the greater, of course, will be its capability of resistmg 
the usual process of decay. 
The following Table (drawn up chiefly from the researches of M. 
Hugard) shews, approximatively, the amount of inorganic matter in 
various animal bodies, and is thus of interest in a paleontological 
point of view: 
Inorganic matter, 99 or more, per cent. :—Shells of Ostrese and of 
some other acephalous mollusks. 
Inorganic matter, 95 to 98 per cent.:—Most coral structures ; 
shells of ordinary bivalves and gasteropods. 
Inorganic matter, 90 to 95 per cent.:—Shells of ordinary cepha- 
lopods. } 
Inorganic matter, 60 to 70 per cent.:—Teeth of mammals, rep- 
tiles, and many fishes. 
Inorganic matier, 50 to 66 per cent.:—Bones of mammals, birds, 
and reptiles; scales of fishes; shells of crustaceans. 
Inorganic matter, 40 to 50 per cent. :—Elytra of certain insects (?). 
Inorganic matter, under 5 or 6 per cent. :—Scales of reptiles ; car- 
tilage, hair, horns, and nails of mammals; feathers of birds, &e. 
Fossilized Vegetable Remains :*—The fossil plants obtained from 
* It will of course be understood that we are not attempting, here, an Essay on Palzeonto=» 
logy. Our object is chiefly to convey to the uninitiated reader such an amount of informa- 
tion as will enable him to understand the terms of general employment in paleontological 
descriptions, and to obtain a proper conception of the natural relations and positions of our 
more common and characteristic fossil types. We have therefore sought to condense as nuch 
as possible, and to avoid all matters not immediately connected with the end in view. 
