304 
IMPEKFECTION OF THE 
Chap. IX. 
remarks, and to show how liable we are to error in 
supposing that whole groups of species have suddenly 
been produced. I may recall the well-known fact that 
in geological treatises, published not many years ago, 
the great class of mammals was always spoken of as 
having abruptly come in at the commencement of the 
tertiarv series. And now one of the richest known accu- 
«/ 
mulations of fossil mammals, for its thickness, belongs 
to the middle of the secondary series; and one true 
mammal has been discovered in the new red sandstone 
at nearly the commencement of this great series. Cuvier 
used to urge that no monkey occurred in any tertiary 
stratum; but now extinct species have been discovered 
in India, South America, and in Europe even as far back 
as the eocene stage. Had it not been for the rare acci¬ 
dent of the preservation of footsteps in the new red 
sandstone of the United States, who would have ven¬ 
tured to suppose that, besides reptiles, no less than at 
least thirty kinds of birds, some of gigantic size, existed 
during that period? Not a fragment of bone has been 
discovered in these beds. Notwithstanding that the 
number of joints shown in the fossil impressions corre¬ 
spond with the number in the several toes of living- 
birds’ feet, some authors doubt whether the animals 
which left the impressions were really birds. Until 
quite recently these authors might have maintained, 
and some have maintained, that the whole class of birds 
came suddenly into existence during an early tertiary 
period; but now we know, on the authority of Professor 
Owen (as may be seen in Lyell’s ^ Manual’), that a bird 
certainly lived during the deposition of the upper green¬ 
sand. 
I may give another instance, which from having passed 
under my own eyes has much struck me. In a memoir 
on Fossil Sessile Cirripedes, I have stated that, from the 
