4 THE PRESIDENTIAL ADDRESS 
of continents, far removed from the oceans of the present day, and 
thus indicating important and repeated changes in the position of 
land and water ; and, secondly, the deformation of these flat deposits 
till they were rucked and ridged to build the mountain ranges. 
Before and since Lyell’s time geologists have devoted themselves 
to working out the exact and detailed succession of these stratified 
rocks, translating their sequence into history and their characters 
into terms of geography; the succession of physical conditions 
prevailing at the time of their formation. Further, although animals 
and plants migrate from place to place, the time occupied by the 
migrations of suitable forms is so negligible when compared with 
the length of the chapters of geological history that their fossil 
remains have proved to be the best means for correlating strata 
over broad stretches of the earth’s surface. ‘This correlation has 
converted the fragments of local history thus revealed into at least 
the outlines of the geological story of the world. 
It was not till 1885, however, that the accumulation of data of 
this type was sufficient to enable the great geologist, Suess, an 
Austrian but born in this country, to assemble and correlate them, 
and to deduce from them further principles which have been the 
mainstay and inspiration of his successors. We owe to Hertha 
Sollas and her father the rendering of this great work, The Face of 
the Earth, into English ; and to Emmanuel de Margerie and his 
colleagues a French translation enriched with a magnificent series 
of maps and sections such as could only have been brought together 
by one with the most remarkable bibliographic knowledge; a 
veritable recension of the original. 
The nature and associations and the distribution in time and space 
of modern changes in the relative levels of land and sea, as detected 
at sea-margins and by altitude survey, and of older changes betrayed 
by such evidence as submerged forests and raised beaches, had 
convinced geologists that the unstable element was not the fickle 
and mobile sea, but the solid if elastic earth-crust. They naturally 
applied the same explanation to those encroachments of the sea in 
the past which had resulted in the formation of our stratified rocks. 
But while some investigators were content with one form of move- 
ment—that due to lateral pressure—to explain both the formation 
of mountains and the rise and fall of the land, others called in a 
different cause for the latter. Without entering into a discussion of 
causes it may be well for us to distinguish the orogenic or mountain- 
forming from the epeirogenic or continental movement. 
The evidence collected by Suess proved that these last great land 
and sea changes had occurred simultaneously over whole continents 
or even wider regions. Such great submergences as those to which 
the Cambrian Rocks, the Oxford Clay, and the Chalk are due were 
