20 The American Naturalist. [January, 
bringing with them a train of mineralogical accidents as a 
necessary accompaniment in the percolation of mineral waters 
and the solidification of the natural cement which surrounds 
the fossils have contributed towards rendering these remains 
impenetrable. I do not know how the petrifaction of bone 
compares with the silification of wood, either as a process or 
in the time required, but it is certain that, in some instances, 
teeth have been completely changed into a mineral, as in the 
case of the saurian teeth found by Mr. C. M. Wheatley in a 
bone bed at Pheenixville, Pa. Here, to quote Mr. Wheatley’s 
own words, “ the casts only of the teeth remain, the substance 
of the tooth being converted into dolomite, but retaining the 
exact form of the tooth with the sulcations as distinct as in the 
original. Twenty teeth, of probably three or four genera of 
Saurians, all converted into dolomite occur on a piece of sand- 
stone six by three inches.” 
Bischof, quoting the results of Marcel de Serres and L. 
Figuier, says that the chemical changes involved in the petri- 
faction of bones consist principally in a diminishment of the 
organic matter, in an entire disappearance of the phosphoric 
acid, and in an increase of the carbonate of lime and iron 
oxide. 
Again, Fremy found that the animal substance of bones— 
the so-called ossein—was decomposed by burial and replaced 
by various incrusting minerals, namely, silica, sulphate of 
lime, fluoride of lime, and especially carbonate of lime. 
Dr. Mantell has made some interesting observations on the 
mineralization of bones. He remarks (Petrifactions and their 
Teachings) of the bones of reptiles that “the osseous carapaces 
and plastrous of the turtles, and the bones and teeth of the 
crocodiles and lizards, are almost without exception heavy, 
and of various shades of brown or umber, from the permeation 
of their structures by solutions of carbonates or oxides of iron.” 
Mantell refers to the curious appearance of bones imbedded in 
white limestone, which have become a blue-black from the 
combination of their phosphoric acid with iron, forming the 
blue phosphate of iron (vivianite), while in other cases the 
~ Pi P< oe eT E ed =< i 
ee Oe ere ye S 
y a ah Re ee RE NT eee ep eee 2 
open surfaces and cells are infiltrated with cale-spar or reful- J 
gent with a golden frost of iron pyrites, 
