240 
THE GEOLOGIST. 
old regenerated sediments of its shore?. Eut it is only over very small 
areas that this determination — whieli only requires time and labour 
to complete for the whole — has been efteetcd. T\'e can accomplish this 
for England and Korth America ; we might do it for Europe and 
South America ; hut for the great tracts of Asia and Africa it would 
,be, as yet, impracticable. Still we have learned enough to know that 
the present great ridges and mountain-chains of our continental lands 
arc generally the same ridges that first rose above the primeval sea, 
and that, if repeated have been the depressions and elevations of our 
continents, those depressions and elevations have been chiefly along the 
same lines of fracture and of weakness from primeval times to our own. 
Wo have learned enough to know that those first lands were less 
extensive than those broad tracts around us, and lower; that, from 
beneath an unbounded sea, wraj)ping the globe as in a mantle, the first 
granitic and gneissic bosses rose as broad low islands from which the 
wild waves, beating upon and wearing them down derived and de- 
posited on the more sheltered coasts the vast thicknesses of gneissic mud, 
primeval conglomerate, and those sediments which are now the " bottom- 
rocks." "With the continued rise of these island-crowns and ridges, 
the first sediments were also, in time, gradually raised, and the shores 
became broader and shallower with the expansion of the uprising tracts, 
until the period of those wide-spreading mud-shores on which the 
Silurian molluscs and " creeping things" lived in myriad-shoals. Thus, 
in the first age, the division of the waters which covered the globe into 
our present oceans and seas was shadowed out, and thus, as the ever 
accumulating sediments, band after band, spread wider and wider 
through successive geological periods around island-lands and ridges, 
at length the dclris of the land gained its conquest over the restless 
waters by linking those accumulations together. 
As age after age passed away, bauds upon^^bands of sediments widened 
the extent of earth-surface, and by gradual elevation the oldest 
land rose into higher tracts, the drainage of which, by a similar gradual 
progress of events, gave rise to those rivers whose positions and directions 
are noted by their debris through formation after formation of strati- 
fied deposits, until some of those grand results — often those of time 
and slow processes, sometimes those of violence — cut their traces off from 
the succession of events, and created in particular groups of rocks or 
in special regions, that kind of hiatus which has been viewed, somewhat 
