278 The American Geologist. November, 1902 
to enable a fish of smallish size, say of a foot or two 
in length, to sink into it naturally vmtil partly or com- 
pletely submerged. I say, sink into it naturally, for it is a 
well known fact that these sharks are in every case * preserved 
in the same position, ventro-dorsal, having sunken to the bottom 
doubtless with belly upward, still partly distended with gases. 
The bottom-sediment, accordingly, was soft and fine. It was 
also probably deep, since in some cases the sharks have sunken 
into it completely, the well preserved fins passing out of the 
general plane of the fossil into an overlying portion of the 
matrix. Moreover the sediment could have been, subject to 
no extensive movements, since these sharks, although collected 
over a wide area, show no evidence of having changed position 
(i. e., rolled) from the time they first sank to the bottom. 
Surface currents, on the contrary, may well have been 
present, since in the shale the remains of fishes with swim- 
bladders are conspicuously rare, in spite of strong evidence 
for believing that they must have been plentiful at that time, 
and even in that region (judging, e. g., from the abundance of 
sharks and from their stomach contents). And we can best 
interpret their rarity in fossils as due to the presence of surface 
currents ; for such types of fishes, unlike sharks,! would float 
during earlier stages of decomposition, and thus, on the as- 
sumption that currents were present, would be carried either 
ashore or to sea, in either case escaping fossilization. 
*A single ifflstance sliould be excepted in \vhich a fish, fossibzed in the usual 
position, shoe's the caudal fin turned on its side. 
fif this evidence be admitted the curious coccostean "fishes" of 
the Cleveland shale are also to be interpreted as lacking- a swim-bladder. 
There is, I Relieve, but little ground for associating them with ganoids 
and lung fishes. 
