240 



THE GEOLOGIST. 



old regenerated sediments of its shores. Eut it is only over very small 

 areas that this determination — which only, requires time and labour 

 to complete for the vrhole — has been effected. We can accomplish this 

 for England and Kcrth. America ; we might do it for Europe and 

 South America ; but 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 

 are 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. 

 ^Ye 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, wrapping 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 these 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 v/as 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 deiris of the laud gained its conquest over the restless 

 waters by linking those accumulations together. 



As age after age passed away, bands 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 

 arc noted by their dehru through formation after formation of strati- 

 fied deposits, until some of tliose 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 rogiony, that kind of hiatus which has been viewed, somewhat 



