impressions of the joints of a backbone and of the armour of a great
reptile, twelve or more feet long. This great beast had died and got
buried in the sand; the sand had gradually hardened over the bones, but
remained porous. Water had trickled through it, and that water being
probably charged with a superfluity of carbonic acid, had dissolved all
the phosphate and carbonate of lime, and the bones themselves had thus
decayed and entirely disappeared; but as the sandstone happened to have
consolidated by that time, the precise shape of the bones was retained.
If that sandstone had remained soft a little longer, we should have
known nothing whatsoever of the existence of the reptile whose bones it
had encased.

How certain it is that a vast number of animals which have existed at
one period on this earth have entirely perished, and left no trace
whatever of their forms, may be proved to you by other considerations.
There are large tracts of sandstone in various parts of the world, in
which nobody has yet found anything but footsteps. Not a bone of any
description, but an enormous number of traces of footsteps. There is
no question about them. There is a whole valley in Connecticut covered
with these footsteps, and not a single fragment of the animals which
made them has yet been found. Let me mention another case while upon
that matter, which is even more surprising than those to which I have
yet referred. There is a limestone formation near Oxford, at a place
called Stonesfield, which has yielded the remains of certain very
interesting mammalian animals, and up to this time, if I recollect
rightly, there have been found seven specimens of its lower jaws, and
not a bit of anything else, neither limb-bones nor skull, or any part
whatever; not a fragment of the whole system! Of course, it would be
preposterous to imagine that the beasts had nothing else but a lower
jaw! The probability is, as Dr. Buckland showed, as the result of his