The variability of the matrix and of the color and condition of the bones indicates that the agencies of burial and fossilization differed from time to time and that the agency of transportation of the bones from the site of burial to the fissures was running water.
"Two New Pelycosaurs from the Lower Permian of Oklahoma"
Richard C. Fox
A large proportion of aquatic creatures have structures which do not admit of fossilization; while of the rest, the great majority are destroyed, when dead, by various kinds of scavengers.
"Essays: Scientific, Political, & Speculative, Vol. I"
Herbert Spencer
The exact manner in which this replacement is effected and in which the chemical and mechanical changes occur is very far from being definitely known-especially as the process of "fossilization" must at times have been very complicated.
"Animals of the Past"
Frederic A. Lucas