316 Proceedings of the Royal Physical Society. 



rentian, or whether the Cambrian occupied a longer time in 

 formation than the overlying Silurian. We may feel con- 

 vinced, from the total thickness of a system, the alterna- 

 tions of its strata, and the succession of its fossils, that it 

 occupied a much longer time in formation than another sys- 

 tem ; but this is not expressed in the above arrangement, 

 which merely affirms a sequence from older to younger, and 

 from the earliest ascertainable operations to those still taking- 

 place around us. 



Such is the chronology of Geology — a chronology to which 

 investigators endeavour to conform the rock-formations of 

 the globe ; and although the Chalk of one country, for ex- 

 ample, may not have been exactly contemporaneous with 

 the Chalk formation of another region, still we know that 

 it stands intermediate between the Oolite and Tertiary, and 

 can therefore assign to it a place relatively to these forma- 

 tions. In some region yet unexplored a whole suite of 

 strata may be discovered older than our Carboniferous, and 

 yet younger than our Old Eed, and in such a case geologists 

 would give the new formation a name, and place it as inter- 

 mediate between these two systems. It would disturb no 

 established order, but merely render more complete the 

 sequence, like the interpolation of a hitherto unknown reign 

 in the dynasties of human history. The geological record 

 is thus a thing of mere sequence — an inconceivable amount 

 of unexpressed time, during which certain events follow each 

 other in definite order. How many ages have elapsed since 

 the first deposition of the Laurentian strata we cannot tell ; 

 how many centuries were spent in the formation of the 

 Coal-measures of any locality, we can only, estimating from 

 existing operations, offer the widest conjecture. But we 

 can affirm with certainty, and this is a great point gained, 

 that one rock-system is younger than another ; that these 

 rock-systems follow in the order above given ; that accord- 

 ing to our present knowledge invertebrate life preceded the 

 vertebrate ; that fishes preceded reptiles, reptiles birds, and 

 birds mammalia. We can also affirm, what it is the object 

 of the following remarks to prove, that as there has been an 

 ascent in time from lower to higher forms of life, so Man, 



