232 EXTINCT MONSTERS 
the world’s extinct races which has taken place during the last 
quarter of a century ought to make us careful with regard to 
broad statements of the above kind, which may require to be 
modified by future discoveries. 
Now, the tendency of all the later results of Paleontology is 
to show that some of the higher types of life appeared on the 
earth a good deal earlier than was formerly supposed. Thus 
the discovery of the jaw-bones of small mammals (possibly 
marsupials) in the Purbeck strata, in 1854, and afterwards in the 
Stonesfield slate (both of Jurassic age), came as a surprise to 
most geologists. Again, it is not long since birds were believed 
to have come into existence only in Tertiary times: now we 
have the Jurassic bird Archzopteryx (see p, 212), and Professor 
Huxley has recorded his opinion that some of us may live to see 
a fossil mammal of the remote Silurian age! It is, therefore, 
only prudent for geologists to be on their guard against assuming 
that all the Secondary mammals were of low types and few in 
numbers, as might be inferred from the phrase “ Age of Mammals.” 
That mammals, however, developed vigorously in many directions 
during the Tertiary era cannot be doubted. So, far, then the 
expression conveys important truth; but in science, as in other 
things, the “unexpected” often happens, so it is better to be 
prepared for surprises. 
It would be impossible within the limits of a single chapter to 
give an account of all the leading orders of Tertiary mammals. 
We must therefore limit our present remarks to two or three, 
or more, reserving others for future chapters. 
The discovery, in the early part of the present century, of the 
rich treasures embedded in the Tertiary strata of the Paris basin, 
and the consummate skill with which they were interpreted and 
restored by the immortal Cuvier, gave a very great impulse to the 
