THE GROWTH OF CONTINENTS. loT 
epoch, and it is here that my own share in the 
work, such as it is, belongs. 
Accustomed as a boy to ramble about in the 
beautiful gorges and valleys of the Jura, and in 
riper years, as my interest in science increased, 
to study its formation with closer attention, this 
difference in the inclination of the slope had not 
escaped my observation. I was, however, still 
more attracted by the fossils it contained than by 
its geological character : and, indeed, there is no 
better locality for the study of extinct forms of 
life than the Jura. In all its breaks and ravines, 
wherever the inner surface of the rock is exposed, 
it is full of organic remains ; and to take a hand- 
ful of soil from the roadside is often to gather a 
handful of shells. It is actually built of the re- 
mains of animals, and there are no coral reefs in 
existing seas presenting a better opportunity for 
study to the naturalist than the coral reefs of the 
Jura. Being already tolerably familiar with the 
fossils of the Jura, it occurred to me to compare 
those of the upper and lower slope ; and to my 
surprise I found that they were everywhere dif- 
ferent, and that those of the lower slope were in- 
variably Cretaceous in character, while those of 
the upper slope were Jurassic. In the course of 
this investigation I discovered three periods in 
the Cretaceous and four in the Jurassic epoch, 
all characterized by different fossils. This led to 
a more thorough investigation of the different 
