
INTRODUCTION. 5 
beds have subsequently been crumpled, contorted, dislocated, invaded 
by igneous masses from below, and rendered sometimes intensely 
erystalline. It teaches, too, that wherever exposed above sea-level 
they have been incessantly worn down, and have often been depressed, 
so that older came to be buried beneath later accumulations. 
5. Palzontological Geology.—This branch of the subject deals 
with the organic forms which are found preserved in the rocks of the 
erust of the earth. Jt includes such questions as the relations 
between extinct and living types, the laws which appear to have 
governed the distribution of life in time and in space, the value 
of fossils and the relative importance of different genera of animals 
and plants in geological inquiry, and the nature and use of the 
evidence from organic remains regarding former conditions of 
physical geography. : 
6. Stratigraphical Geology—This section might be called geo- 
logical history. It works out the chronological succession of the 
great formations of the earth’s crust, and endeavours to trace the 
sequence of events of which they contain the record. More 
particularly it determines the order of succession of the various 
plants and animals which in past time have peopled the earth, and 
thus ascertains what has been the grand march of life upon the 
lanet. 
2 7. Phystographical Geology, starting from the basis of fact laid 
down by stratigraphical geology regarding former geographical 
changes, embraces an inquiry into the history of the present features 
of the earth’s surface—continental ridges and ocean basins, plains, 
valleys, and mountains. It investigates the structure of mountains 
and valleys, compares the mountains of different countries and 
ascertains the relative geological dates of their upheaval. It 
explains the causes on which local differences of scenery depend, 
and shows under what very different circumstances, and at what 
widely separated intervals, the varied contours, even of a. single 
country, have been produced. 
