1897.} Fossils and Fossilization. 23 
may have prevailed, little else than the hardest portions of the 
fish were preserved as the dermal tubercles, spinesand armored 
heads, with an occasional jaw retaining its teeth. Even this 
slender survival of material compares favorably with the de- 
structive activity of our seas, and may perhaps add weight to 
the opinion of Verrill and Smith that this destruction to-day 
can be only assigned to the depredations of small crustacea. 
It also lends some seriousness to suspicions that in these pale- 
eozoic waters deposition was more rapid than at present. But 
in the fish layers of Boonton, N. J. and Sunderland, Mass., in 
the Triassic slates and in the thinly fissile lime shale of Twin 
Creek, Wyoming, we find an extensive placement of fish skel- 
etons and bodies which are usually quite perfect in outline 
and which must have been deposited almost simultaneously 
by some sudden catastrophe, and also very rapidly sealed 
within fresh sediment, in which they remained undisturbed 
by the motion of the water, and protected against change by 
the overlying films of calcareous mud. Dr. Newberry has 
suggested that in the case of the triassic fish their death was 
connected with the irruption of hot waters produced by the 
intrusion of the igneous trap rocks through the floor of the 
triassic sea. The similar beds at Weehawken, N. J., show that 
the fish have undergone considerable maceration and distor- 
tion, and the subsequent breaking of these slates have helped 
to obliterate the organic remains. The Twin Creek fish bed 
is a compilation of very thin sheets of flaky limestone with 
clay, between whose slightly undulating surfaces runs a wav- 
ing black film, the section of a slab presenting a delicately 
lined face like a paper pencilled with parallel tracings. Here 
the fish lie with very slight dislocation appearing ; to use Dr. 
Leidy’s words, “as if whole shoals had been suddenly en- 
shrined for the contemplation of future ages.” It would seem 
as if an innumerable series of overflows, each carrying with it 
floculent carbonaceous matter, had left a deposit of carbonate | 
of lime from suspended particles over the fish, and, as each 
overflow receded, these fine particles followed the absorbed 
water and remained upon the surface in a veil of black sedi- 
ment. It may be that a sudden irruption of water carrying 
