4.96 TRANSACTIONS OF SECTION C. 
III. The Deep-seated Control over the Earth's Surface. 
The modern view of the structure of the earth adds greatly to the interest of 
its study, for it recognises the world as an individual entity of which both the 
geological structure and the history have to be considered as a whole. Once the 
earth was regarded as a mere lifeless, inert mass which has been spun by the 
force of gravity that hurls it on its course, into the shape of a simple oblate 
spheroid. Corresponding with this astronomical teaching as to the shape of the 
world was the geological doctrine, that all its topography is the work of local 
geographical agents, whose control over the surface of the earth is as absolute as 
that of the sculptor’s chisel over a block of marble. 
Both these conceptions are now only of historic interest. The irregular indi- 
vidual shape of the earth is expressed by its description as a geoid. The pro- 
cesses which have produced its varying shape have also controlled its geological 
history and evolution, for they cause disturbances of the crust, which affect the 
whole earth simultaneously ; and so the geographical agents are given similar 
work and powers at the same time in different places. 
Hence there is a remarkable world-wide uniformity in the general characters 
of the sedimentary deposits of each of the geological systems. The last pre- 
Cambrian system includes thick masses of felspathic sandstones alike in the 
Torridonian of Scotland, the sparagmite of Scandinavia, the Keweenawan Sand- 
stones of the United States, and perhaps also the quartzites of the Rand. The 
Cambrian has its greywackes and coarse slates and its numerous phosphatic 
limestones; the Ordovician its prevalent shales and slates; the Silurian its epi- 
sodal limestones and shales. The Devonian has its wide areas of Old Red Sand- 
stones as a continental type, while its marine representatives show the prevalence 
of coarse grits and sandstones in the lower series, of limestones and slates in 
the middle series, and the recurrence of sandstones in the upper series; and 
this sequence occurs alike in North-Western Europe, in America, and Australia. 
The Carboniferous contains the first regional beds of thick limestone and the 
first important Coal Measures. The Trias contains rocks indicating the same 
arid continental conditions in America, Australia, Asia, and Africa that Pro- 
fessor Watts has shown then prevailed in the neighbourhood of Leicester. 
In the Mesozoic era we owe to Suess the demonstration of the world-wide 
influence of those marine encroachments or ‘ transgressions’ whereby the great 
continents of the Trias were gradually submerged by the rising sea. 
Speaking generally, there is a remarkable lithological resemblance between 
contemporary formations in all parts of the world. This fact had been often 
remarked, but was usually dismissed as due to a number of local isolated coinci- 
dences of no special significance. But the coincidences are too numerous and 
too striking to be thus lightly dismissed. They are among the indications that 
the main earth-changes have been due to world-wide causes, which led to the 
predominance of the same types of sedimentary rocks during the same period in 
many regions of the world. 
The conditions that govern the geological evolution and general geography of 
the earth are probably due to the interaction between the earth’s crust and the 
contracting interior; they may take place as slow changes in the form of the earth, 
causing the slow rising or lowering of the sea surface, or the slow uplift or depres- 
sion of regions of the earth’s erust; or they may give rise to periods of violent 
volcanic action in many parts of the earth, between which may be long periods of 
quiescence. The geographical effects of changes in the earth’s quivering mass 
affect distant regions at the same time. Therefore the landmarks of physical 
geology will probably be found to give more precise evidence as to geological 
synchronism than those of Paleontology, on which we have hitherto had to rely. 
IV. Plutonists and Ore-formation. 
Belief in the earth’s internal fires was most faithfully held amongst 
geologists by the Plutonists of the eighteenth century, and repudiated with 
