220 
THE RHAETIC BONE BEDS 
free from teeth and seales ! The “ True Bone Beds ” 
always have a fair proportion of bones, more or less 
broken. 
The first four eonstituents (bones, teeth, scales, and 
coprolites) can be grouped together, and attributed to 
three classes of animals : 
(1) Saurians, of which Plesiosaurus is decidedly the 
most plentiful, with Ichthyosaurus in much smaller num- 
bers. (There are other and rarer kinds, but as this 
paper is not intended to be a list of fossils, only the more 
prominent will be noticed.) 
(2) Fishes, of which the most plentiful are Hyhodus, 
Nemacanthus, Saurichthys, Gyrolepis, Sargodon, Acrodus, 
and last, but not least, the great mud-fish Ceratodus. If 
the size of the teeth of the latter is any criterion, this must 
have been some 15 or 20 feet long. This fish has been 
erroneously termed a vegetarian, the fact being it will 
eat anything, especially dead fish. 
(3) Amphibians. The representative of this class in- 
clude only one animal, known as “ Metoposaurus ” or 
“ Metopias,^^ a curious complex beast, “ half toad and 
half alligator,” belonging to the Labyrinthodonts. 
Now we come to the fifth constituent. Quartz pebbles, 
the occurrence of which opens up a most interesting ques- 
tion. The fact is, that wherever we get these animal 
remains we also find the pebbles intermixed with them, 
and this quite independently of the adjacent rock, whether 
limestone, sandstone, clay, or marl. Where the Bone 
Bed is, there also are these pebbles ! 
It has been suggested that these pebbles were drifted 
or water borne to the localities where we now find them, 
but a careful examination of the facts soon disposes of the 
drift theory ; the absence of any traces of erosion, the 
position of the fossils, and their extraordinary freedom 
from scratches and abrasions, all militate against this 
