THE ICHTHYOSAURUS. 158 
followed by man in building steam vessels, where the centre of 
the moving force is placed in front of the centre of gravity; and 
in the Ornithorhynchus, to which I before alluded, the membranous 
expansion of the fore feet greatly exceeds that of the hind feet. 
The arrangement therefore made it much easier for the animal to 
ascend from great depths to the surface in order to obtain a fresh 
supply of air, and this action was further facilitated by the form 
and arrangement of the breast bone and others to which the 
muscles were attached, and which are almost identical with those 
obtaining in the Ornithorhynchus. The only organ for me to 
notice, in conclusion, is the tail, which was very long, and flattened 
at the extremity, thus assisting the huge animal in propelling 
itself through the water, 
Henry ULtyett. 
Hollow Lane,* 
T is scarcely necessary to remind you that the whole of the 
terra firma upon which we now stand, and which stretches 
away to the distant horizon, was once under watet, forming the bed 
of a very deep sea. This fact is evident to the merest casual ob- 
server of our chalk pits; finding in them numerous remains of 
what are popularly called shell-fish, and of such only as exist in 
salt water, he naturally and correctly says that the salt water 
once covered these valleys and hills. And not only so, but he 
must also come to the conclusion that these hills themselves have 
been formed in the sea water, or else how do we account for the 
fact that the organic remains are found in all positions and at all 
depths from the surface? ‘The chalk could not have been there 
before the shells; no, the shells were there, and the chalk 
* Read before the Society on the third Field-day of the First Summer 
Session, Aug. 28, 1865. 
