102 
NATURE NOTES. 
species and varieties, as do roses, blackberries, willows, &c. ; 
others vary little, or remain monotypic. 
The doctrine of evolution is based, not on negative but on 
positive evidence, and in no way is it controverted by the 
presence of survivals. 
As the fossil remains of animais are so much more numerous 
than those of plants, because of the very perishable nature of 
the latter, they afford plenty of illustrations of survivals, as the 
following examples will show. 
When Sir Charles Lyell studied the various strata which 
represent the Tertiary Epoch, he noticed that in the lowest 
“ formation,” which he called the “ Eocene” or “ Dawn of the 
New ” as the word means, about 4 per cent, of shells which 
are still living. In the next two formations which he called 
“ Miocene ” and “ Pliocene ” he found increasing percentages of 
recent or living species of shells. They therefore showed 
respectively a “ less new” and a “ more new ” condition ; so he 
called them by those names. Lastly, came the uppermost or 
“ Pleistocene,” the “ most new,” in which the percentage of 
extinct species of shells was now much in the minority. 
Here, then, we have existing species of shells running back 
into probably hundreds of thousands of years. But we may go 
further backwards in time. The uppermost strata of the 
Secondary Epoch are the beds of chalk, which is made up of 
the remains of microscopic shells of species of Foraminifera, one 
at least of which is still living ; so that the late Dr. W. B. 
Carpenter used humorously to say “ we are still living in the 
Cretaceous Epoch ! ” But that is not enough. Passing over 
survivals from the oolitic beds, such as the shell Trigonia, cycads 
and crocodiles, let us go back to the Primary Epoch. I will 
first give two illustrations from the so-called Devonian formation. 
Before fishes represented the highest efforts of evolution, gigantic 
shells ruled the marine world, and were especially represented 
by the great family Nautilidae. One genus, nautilus, has lived 
on till to-day. On the other hand the Ammonitidae which was 
descended from and supplanted the former family, cannot boast 
of a single survival. When the reign of the Nautilidae was 
over, fishes took the lead, and very unlike the fishes of to-day 
they were. Many had no backbones, only an embryonic gela- 
tinous spinal cord, illustrating a universal rule that animals of 
an early geological period, when adults have features resembling 
the young, or even the embryonic condition of members of the 
same family of later geological times. At least three kinds of 
these curious old fishes are living still. 
Lastly, let us proceed one step backwards to nearly the most 
primitive times. If we climb up the side of Snowdon’s great rival, 
Cader Idris, overlooking Barmouth, we shall find slates strewn 
about covered with impressions of a species of lingula, and as 
far as those impressions can tell us, there seems little to distin- 
guish them from the living lingula of to-day. 
