18 EXTINCT MONSTERS 
at first, but the proofs are quite convincing.’ As Professor 
Huxley well remarked, there is as good evidence that chalk has 
been built up by the accumulation of minute shells as that the 
Pyramids were built by the ancient Egyptians. 
The science of geology reveals the startling fact that all the 
great series of the stratified rocks, whose united thickness is over 
80,000 feet, has been mainly accumulated under water, either by 
the action of those powerful geological agents—rain and rivers— 
or through the agency of myriads of tiny marine animals. When 
we have grasped this idea, we have learned our first, and perhaps 
most useful, lesson in geology. 
Now let us apply what has been above explained to the 
question immediately before us. We want to know how the 
skeletons of animals living on land came to be buried up under 
water, among the stratified rocks that are to be seen all over our 
country, and most of which were made under the sea. 
We can answer this question by going to Nature herself, in 
order to find out what is actually going on at the present time, 
by inquiring into the habits of land animals, their surroundings, 
and the accidents to which they are lable at sundry times and 
in divers manners. It is by this simple method of studying 
present actions that nearly all difficult questions in geology may 
be solved. The leading principle of the geologist is to interpret 
the past by the light of the present; or, in other words, to find 
out what happens now, in order to learn what took place ages 
ago; for it is clear that the world has been going on in the same 
way for at least as far back as geological history can take us. 
There has been a wniformity, or sameness, in Nature’s actions 
ever since living things first dwelt on the earth. 
Just as rivers are mainly responsible for bringing down to the 
1 See the writer’s Autobiography of the Earth, p. 223. 
