260 THE CAUSES WHICH 



occupied by the Thames and confluents. We may show that 

 gene rail)/ the eastern shores of England and North America are 

 sinking"^ while that of the Baltic is rising-, and this also at a 

 definite rate of a foot a century, and so forth. We may also 

 mentally work out through long geologic ages, the action of this 

 twofold minister of change and destruction, ever silently heaping 

 here, the fresh-water accumulations of lakes and rivers on old 

 raised and rising oceanic bottoms, as now over the flat pampas 

 and llanos of America, or over our older valleys of sea limestone 

 and chalk ; and there, salt-water muds with shell and sea tangle 

 on sinking landscapes, as now along the depressing Sussex coast. 

 Or we may note its chronic accelerations and retardation, by the 

 throes of volcano and earthquake, recorded in contortions and 

 upturnings of these sedimentary or stratified rocks that now en- 

 crust like coats of an onion the entire face of the globe, and even 

 infer the comparative age and period of activity of each weathered 

 mountain chain — erst volcanoes, granitic, basaltic, or volcanic — 

 which, at successive periods and in various places, has burst 

 through some of these aqueous rocks, and risen into existence, as 

 in modern time the cindery Monte Gaurus or Jorullo in a night. 

 Gravitation subsequently co-operates with heat in levelling the 

 earth^'s surface ; and as lunar attraction sweeping the tidal waves, 

 it becomes a permanent agent in sculpturing and bevelling the land 

 each time it rises above water-level into islands and continents. 



We will now review the strata containing insect remains in 

 order. From the absence of unequivocally marine fossils and 

 from lithological characters, it is inferred that the Scottish Old 

 Red Sandstone probably originated in inland sheets of water, 

 which Professor Geikie distinguishes as a northern Lake Orcadie, 

 occupying the site of Caithness and Orkney Islands ; a Lake 

 Caledonia, occupying the central valley and basin of the Clyde ; 

 a Lake Cheviot ; a Lake Lome, in the north of Argyllshire ; 

 and the Welsh Lake. The land surface diversified by these 

 ancient sheets of water is stated to have arisen from the shallow- 

 ing of the sea, which became converted here and there into 

 Salinas, or inland seas, by a series of subterranean movements, 

 which have left their indelible traces upon the upturned Silurian 

 rocks, while the now rock metamorphosed sandy material was 

 deposited in their basins during a subsequent general subsidence. 



