26 The American Naturalist. [January,. 
through its minute passages a ferruginous infiltration ap- 
pears, giving it a speckled surface. It seems more than likely 
that much of the original phosphate has disappeared, and 
that carbonate of lime with argillaceous admixture composes: 
the present skeleton. 
The fish of the Twin Creek, Wyoming basin have each 
been immersed in the products of its own decomposition. 
Their bones seem to be, in many instances, covered by an in- 
tegument formed from the dried and mineralized skin and 
scales of the living fish, while the oily elements arising from 
their dry distillation or decomposition have impregnated the 
bones, converting them to a dark honey-brown substance some- 
what laminar in structure, in places, elsewhere irregularly 
cubical, and soft and brittle. The fish in the triassic shales: 
present ichthic outlines made up of rhomboidal scales. These 
scales, as is well-known, are essentially bone, very smooth, 
hard and lustrous, their shining and durable surface being 
formed of a substance allied to enamel and now called ganoin. 
This ganoin has undergone little or no change. The scales 
yield slowly to hydrochloric acid. The original cartilaginous 
or fleshy parts have probably aided preservation by forming 
oily products which bathed the fish, enclosed as it was in the 
shale, and upon dessication contributed their indestructible 
carbonaceous residues to its mass. 
The eretaceous saurians entombed in the gypsiferous shales 
and limestones of Kansas have successfully escaped the action 
of decay, while the remains of sharks, predaceous fish, and tor- 
toises are also found as fossils, but only in a partial phase, at 
least, of preservation. The bones of the fish, who were, accord- 
ing to Cope, related to the salmon, possess such a density and 
hardness that they are maintained as nuclei crowning knobs 
of shale, which stand in relief amidst the worn and denuded 
surfaces about them. This is quite remarkable, and seems to 
clash completely with what we know to-day of the preserva- 
tion, or rather absence of preservation, of the bones of marine 
vertebrates. Prof. Marsh, in speaking of the specimens of cre- 
taceous birds, remarks that “that they are all mineralized and | 
in the same state of preservation as the bones of the extinct 
reptiles which occur with them in these deposits.” 
