430 Darwin, and after Darwin. 
back as the miocene stage. Had it not been for the rare accident 
of the preservation of footsteps in the new red sandstone of the 
United States, who would have ventured to suppose that, no 
less than at least thirty kinds of bird-like animals, some of 
gigantic size, existed during that period? Not a fragment 
of bone has been discovered in these beds. Not long ago 
paleontologists maintained that the whole class of birds came 
suddenly into existence during the eocene period; but now 
we know, on the authority of Professor Owen, that a bird 
certainly lived during the deposition of the upper green-sand. 
And still more recently that strange bird, the Archeopteryx... 
has been discovered in the oolitic slates of Solenhofen. Hardly 
any recent discovery shows more forcibly than this, how little 
we as yet know of the former inhabitants of the world. 
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 stated that, from the number of 
existing and extinct tertiary species; from the extraordinary 
abundance of the individuals of many species all over the world 
from the Arctic regions to the equator, inhabiting various zones 
of depths from the upper tidal limits to 50 fathoms; from the 
perfect manner in which specimens are preserved in the oldest 
tertiary beds; from the ease with which even a fragment of 
a valve can be recognized ;- from all these circumstances, I 
inferred that had sessile cirripedes existed during the secondary 
periods, they would certainly have been preserved and dis- 
covered; and as not one species had then been discovered 
in beds of this age, I concluded that this great group had been 
suddenly developed at the commencement of the tertiary series. 
This was a sore trouble to me, adding as I thought one more 
instance of the abrupt appearance of a great group of species. 
But my work had hardly been published, when a skilful paleeon- 
tologist, M. Bosquet, sent me a drawing of a perfect specimen of 
an unmistakeable sessile cirripede, which he had himself ex- 
tracted from the chalk of Belgium. And, as if to make the case 
as striking as possible, this sessile cirripede was a Chthamalus, 
a very common, large, and ubiquitous genus, of which not one 
specimen has as yet been found even in any tertiary stratum. 
Still more recently, a Pyrgoma, a member of a distinct sub- 
