1897.] Fossils and Fossilization. 21 
In the process of mineralization, which is the last phase of 
the entire process of fossilization, we may imagine that bones 
undergo contrasted changes, according to the varying circum- 
stances of their position. Prof. Leidy has even observed in a 
letter to Dr. Holmes that fossilization, petrifaction or lapidifi- 
cation is no positive indication of the relative age of organic 
remains. The cabinet of the Academy of Natural Sciences of 
Philadelphia contains bones of the megalonyx and of the ex- 
tinct peccary, that are entirely unchanged: not a particle of 
gelatine has been lost, nor a particle of mineral matter added, 
and, indeed, some of the bones of the former even have por- 
tions of articular cartilage and tendinous attachments well- 
preserved. On the other hand, bones of mammals from the 
Keuperkalk near Schweinfurt, Germany, yielded to Von Bibra 
scarcely a trace of phosphoric acid (Bischof); the principal 
constituent was clay. Bones exposed to saturation by water 
which may, or must, contain a very considerable quantity of 
mineral salts in solution, soon surrender their soluble elements 
and undergo a gradual reconstruction amounting, in some 
cases, to complete lithification. The phosphate and carbonate 
of lime may be replaced by silica, or the former may be ex- 
pelled by reaction with alkaline carbonates, and the bone as- 
sume more and more entirely the composition of carbonate 
of lime. 
The circumstances attendant upon the fossilization of inver- 
tebrates necessarily contrasts strongly with those observed in 
the fossilization of vertebrates. Invertebrates—corals, mol- 
lus, crustacea—are more usually the inhabitants of the salt 
waters, they are sedentary or somewhat limited in the range 
of their voluntary wanderings, their hard parts are almost en- 
tirely carbonate of lime, and at their death their shells or 
coverings are apt to be so situated as to secure more or less 
perfect preservation. The invertebrates which form the largest 
part of the fossil remains of the world are shore occupants, or, 
if removed from land, were living in comparatively shallow 
waters, waters certainly not exceeding 500 fathoms in depth. 
They lived either in the sandy flats or rocky barriers along 
the very margins of the ancient ocean and upon the oscillat- 
