PREFACE. 
HE century now drawing to a close is remarkable 
JL beyond all others for the spirit of inquiry into the 
physical constitution of the earth, into the forces playing 
upon its surface, and into the phenomena of life, both plant 
and animal. The rise of the natural sciences in the modern 
sense may be said to date from its beginning. In this 
great renascence geology has borne an important part. 
It has opened out new and almost endless avenues of 
thought, giving us, on the one hand, the history of the 
ever-changing earth, from the remote time when it was 
sufficiently cool to allow of water resting upon its surface, 
and, on the other, the long and orderly procession of animal 
life beginning with the lowest invertebrate forms and 
ending in Man. In this latter connection it enabled Darwin 
to grasp the principle of evolution that now influences our 
view of life as a whole in the same way as the law of 
gravitation has affected our view of matter, not only in the 
earth, but also in the universe. To us, living at the end 
of the century, it is difficult to realise the conditions under 
which the pioneers lived and worked, because through their 
labours the conditions have wholly changed. In this short 
