139 
not reveal any such finely graduated chain, and this perhaps is 
the most obvious and serious objection which can be urged 
against my theory ;” and again, “the geological record, viewed 
as a whole, is extremely imperfect; but if we confine our 
attention to any one formation, it becomes much more difficult 
to understand why we do not therein find closely graduated 
varieties between the allied species which lived at its com- 
mencement and at its close.” These passages show at once 
Mr. Darwin’s difficulty, for if there be such a thing in nature 
as the evolution of a lower form of animal life into another 
and higher condition, then assuredly we have a right to expect 
to meet with some transition form by which the links of the 
chain are united ; but geology does not reveal any such nicely 
graduated scale, for if it did, none would have presented them 
better than the Lias. I am therefore (said the Doctor) anxious 
to show you the various forms of life which appeared for the 
first time in the Liassic age, and carefully to enquire into the 
ancestry of each of the groups which the Paleontologist has 
discovered in the Lias formation. 
In the upper breccia of the Keuper at Degerloch, Wirtem- 
berg, the molar teeth of a small mammal were found thirty 
years ago, and since then teeth, probably belonging to the same 
genus, have been found in the Lias at Watchet, and near Vallis 
Vale, in Somerset. The animal was probably a small pouched 
quadruped, but anything beyond that is conjecture. It was 
however a true mammal, and the first and oldest known to 
Naturalists. 
The next class to which I invite your attention is the reptiles; 
which, during the Lias age, were the most formidable of all, 
and presented forms of life the most remarkable that we know 
among all the vertebrata. We meet with three distinct groups 
of these in the Lias—the Enaliosawrians, or marine reptiles ; 
the Pterodactyles, or aerial reptiles; and the Teleosawrians, 
or land and river reptiles. Now in each of these groups we 
discover an assembly of anatomical characters which are quite 
special to fit the organism to fulfil the special conditions of its 
existence. Among the first or marine reptiles the Ichthyosaur 
m 2 
