ITS ORDER. 73 



terns," and " groups," and " series" each system being 

 but the sediments of the lakes and seas of a certain period, 

 and characterised, of course, by its own peculiar fossils, as 

 evidence of the life that prevailed during the time of its 

 formation. And the reason is obvious : as land and sea 

 have often changed places the former at one time more 

 insular, at another more continental ; now sitting low and 

 moist in the water, now elevated into lofty and arid re- 

 gions ; subjected at each change to diversity of colder or 

 warmer ocean-currents, to new sets of winds, rains, and 

 other cliniatal conditions each period must necessarily 

 have stamped its own impress on vegetable and animal life ; 

 and so it happens that the great rock-formations (the only 

 records of the world's history) are each characterised by its 

 own peculiar fossils, or facies of animated existence. Thus, 

 when tabulated, these systems and groups present the fol- 

 lowing chronological arrangement : 



BOCK-SYSTEMS. LIFE-PEKIODS. 



POST-TERTIARY, 



TERTIARY, ) 



ICAINOZOIC (Recent Life), 



CRETACEOUS, 

 OOLITIC, . 



TRIASSIC (Upper New Red), 

 PERMIAN (Lower New Red), 



CARBONIFEROUS, 



DEVONIAN (Old Red), . 



SILURIAN, 



MESOZOIC (Middle Life), 



CAM 



BRIAN, 



PALAEOZOIC (Ancient Life), 



METAMORPHIC, HYPOZOIC ( Under Life), ... 



Such are the main stages into which geologists have ar- 



