C 910) 
BOOK VII. 
PHYSIOGRAPHICAL GEOLOGY, — 
AN investigation of the geological history of a country involves 
two distinct lines of enquiry. We may first consider the nature and 
arrangement of the rocks that underlie the surface, with a view to 
ascertaining from them the successive changes in physical geography 
and in plant and animal life which they chronicle. But besides the 
story of the rocks we may try to trace that of the surface itself—the 
origin and vicissitudes of the mountains and plains, valleys and ravines, 
peaks, passes, and lake-basins which have been formed out of the 
rocks, The two enquiries traced backward merge into each other ; 
but they become more and more distinct as they are pursued towards 
later times. It is obvious, for instance, that a mass of marine lime- 
stone which rises into groups of hills, trenched by river-gorges and 
traversed by valleys, presents two sharply contrasted pictures to 
the mind, Looked at from the side of its origin, the rock brings 
before us a sea-bottom over which the relics of generations of a 
luxuriant marine calcareous fauna accumulated. We may be able to 
trace every bed, to mark with precision its organic contents, and to 
establish the zoological succession of which these superimposed sea- 
bottoms are the records. But we may be quite unable to explain 
how such sea-formed limestone came to stand as it now does, here 
towering into hills and there sinking into valleys. The rocks 
and their contents form one subject of study; the history of their 
present scenery forms another. 
The branch of geological enquiry which deals with the evolution 
of the existing contours of the dry land is termed Physiographical 
Geology. ‘To be able to pursue it profitably, some acquaintance with 
all the other branches of the science is requisite. Hence its con- 
sideration has been reserved for this final division of the present work ; 
but only a rapid summary can be attempted here. 
At the outset one or two fundamental facts may be stated. It is 
evident that the materials of the greater part of the dry land have 
been laid down upon the floor of the sea. That they now not onl 
rise above the sea-level, but sweep upwards into the crests of lofty 
mountains, can only be explained by displacement. Thus the 
land owes its existence mainly to upheaval of the terrestrial crust. 
The same sedimentary materials which demonstrate the fact of dis- 
ee 
