THE LIAS MARLSTONE OF LEICESTERSHIRE. 
123 
found (exemplified in the frog), not coiled as in mammals, 
but only slightly bent. There is, however, in the aquatic 
forms no external orifice, for, were the membrane exposed, as 
in mammals, sounds would be intolerable to the animals 
when in water. Abbe Nollet performed many experiments 
to prove this, which he reasoned should be owing to water 
being a better conductor of sonorous vibrations than air. 
Amongst other experiments, he struck together two pieces of 
metal or stone, whilst totally immersed in water, and found 
that the resulting sound sensations were painfully intense. 
Hence the drum in this class is completely covered with skin, 
and its position is only marked by a slight circular depression 
behind and a little below each eye. In these animals the 
otoliths appear to change their character. The stapeolus 
(the smallest of the three otoliths found on either side of the 
head of fish) here elongates into a trumpet-like body—the 
columella—whilst the other two otoliths on each side are much 
diminished, and become partly embedded in the fibres of the 
tympanic membrane. The expanded part of the columella 
forms a kind of disc closing the fenestra ovalis, which, 
like the fenestra rotunda, is found in the vestibule of reptiles. 
Amongst Birds (Ares) the structure of the ear is essentially 
the same as in the higher reptiles. In birds, however, we 
notice a small external orifice, and, in some of the owl tribe, 
a rudimentary concha, or external ear. A distinct cochlea 
exists, resembling that in reptiles. It is divided into two 
passages by a membranous partition, on which the nerve is 
spread out. The tympanum, also, communicates with cavities 
in the cranial bones, which are thus filled with air, and, by 
increasing the extent of surface, would seem to produce a 
more powerful resonance. 
(To be continued.) 
THE LIAS MARLSTONE OF LEICESTERSHIRE AS 
A SOURCE OF IRON. 
BY E. WILSON, F.O.S., CURATOR OF BRISTOL MUSEUM. 
(Continued from page 97.) 
The accompanying map (see Plate II.) shows the outcrop 
of the Marlstone Rock in the Leicestershire district. It is 
based on the lines of the Government Geological Survey, and 
is on the scale of of an inch to the mile. We may, I believe, 
take it as approximately correct; if not absolutely accurate, at 
every point. It must not, however, be imagined that this 
