268 EVOLUTION AND THE PRESENT AGE 
day is reached when none of those remain that once 
were here. How does some form of human speech 
become extinct? About a hundred years ago an old 
lady named Dolly Dentreath died in Cornwall. She 
could speak the Cornish language; after her death 
there was nobody that could. Thus quietly did the 
living Cornish language become a dead language; and 
in a like unobtrusive manner have been wrought most 
of the new becomings which have changed and are 
changing the earth. 
The net result of all this study was that the same 
kind of forces were at work a hundred million years 
ago that are at work to-day, and that the lessons gained 
from our familiar experiences may safely be applied to 
the explanation of phenomena the most remote in time 
as well as in space. In a still more striking degree 
was this exemplified in the researches of Darwin. 
When it became clear that there had been no universal 
catastrophes, it was also clear that the persistence of 
trilobites and other creatures unchanged through suc- 
cessive periods simply showed that they had existed all 
the time because the conditions happened to be favour- 
able. But then it was further noticed that where in 
some given territory one geologic period follows an- 
other, the creatures of the latter period resemble those 
of the earlier much more closely than the creatures of 
some distant region. Thus, through many successive 
periods South America has abounded in animals of 
the general types of armadillo, sloth, and ant-eater. 
For example, although the change from the mega- 
therium of the Pliocene age to the modern sloth is 
greater than the change from a Bengal tiger to kitty 
that purrs on the hearth, yet after all the megatherium 
