40 
DAVIS : FOSSIL FISH EEMAINS. 
stone in which the fossils are preserved, and that during the 
long-er intervals when the intervening- thickness of limestone was 
deposited, there was an almost total absence of fishes in the sea. It 
has already been observed that the limestone is generally a 
homogeneous substance of a more or less crystalline structure, but 
the exploration of the present beds of some of the deep seas 
where chalk or limestone is in process of deposition has proved 
that side by side with the foraminifera which secrete calcareous 
substances, there ai-e others which have a more or less siliceous 
skeleton and that the latter constitutes a portion of the substance 
forming the sea bottom. One of the peculiarities in connection with 
the great aggregation of fish-remains in the Red Beds of Wensley- 
dale is, that the beds are extremely cherty, masses of nodular chert 
extend in horizontal layers in close proximity with the fish-beds. The 
method by which the nodules and beds of chert have been separ- 
ated is not understood ; it is possible that the presence of submarine 
thermal springs, due to volcanic action, may have something to 
do with the aggregation of the silica to form the cherty or flinty 
masses. If such be the case, it might be equally probable that 
the ebullition of water, charged with perhaps poisonous ingredients, 
would result in the destruction of large numbers of fishes, and in 
this way the fish-beds may have originated. Except on some 
hypothesis such as this, it is difficult to conceive a good reason 
for the occurrence of immense numbers of fish-remains on definite 
horizons of small thickness, and their almost total absence through- 
out great thicknesses of intermediate limestone. 
Notwithstanding the extreme localization of the beds contain- 
ing fish-remains there is no reason to complain of the numbers of 
either specimens or species in localities where they do occur and 
have been carefully collected, but as will be observed further on, 
the characteristics of the Yorkshire Limestone fishes are peculiar. 
In many respects they are distinguished from those, either of the 
limestone of other localities of the British Islands, or of the coal 
measures which succeeded them. 
