666 THE POPULAR SCIENCE MONTHLY. 



species of animals change is tolerably uniform. The fossils of one 

 age differ but little from those of ages immediately preceding and 

 following it. We must go back, he says, to a period when the marine 

 shells differ as a whole from those now existing to form one complete 

 period. Counting back in stages measured by changes of fossils, we 

 have four such stages in the tertiary formations above the chalk. 



Lyell saw reason to believe, on evidence which we shall presently 

 examine, that the age of ice commenced about a million of years ago. 

 The place of this age of ice among the series of fossil-changes is easily 

 marked, and so he concludes that each of his four periods above the 

 chalk " would lay claim to twenty millions of years." We must 

 allow Sir Charles to work up to his stupendous conclusion in his own 

 words : 



" Theantecedent Cretaceous, Jurassic, and Triassic formations would yield us 

 three more epochs of equal importance to the three Tertiary periods before 

 enumerated, and a fourth may be reckoned by including the Permian epoch 

 with the gap which separates it from the Trias. In these eight periods we 

 may add, continuing our retrospective survey, four more, namely, the Carbo- 

 niferous, Devonian, Silurian, and Cambrian ; so that we should have twelve in 

 all, without reckoning the antecedent Laurentian formations which are older 

 than the Cambrian. ... If each, therefore, of the twelve periods represents 

 twenty millions of years on the principles above explained, we should have a 

 total of two hundred and forty millions for the entire series of years which have 

 elapsed since the beginning of the Cambrian period." 



Eighty millions since the lower tertiary formation, one hundred 

 and sixty millions since the formation of the coal-measures, and two 

 hundred and forty millions since the beginning of the Cambrian pe- 

 riod ! And beyond that inconceivable antiquity lie the whole range 

 of the primary rocks which contain no fossils. 



Mr Darwin 1 assigns to the world even a greater age. " In all prob- 

 ability," he says, " a far longer period than three hundred millions 

 of years has elapsed since the latter part of the secondary period." 

 Other geologists exceed even this estimate. ]\Ir. Jukes, for instance, 

 after referring to this passage, in which Mr. Darwin has given an esti- 

 mate of the length of time necessary for wearing down the space be- 

 tween the North and South Downs, declares it is just as likely that 

 the time which actually elapsed since the first commencement of the 

 erosion, till it was nearly as complete as it now is, was really a hun- 

 dred times greater than his estimate, " or thirty thousand millions of 

 years ! " 



To any one but a professed geologist, it would almost seem as if 

 these ideas of geological periods had been framed on the principle 

 which guided Mr. Montague Tigg in fixing the capital of the Anglo- 

 Bengalee Disinterested Loan and Life-insurance Company. " What," 

 asked the secretary, "will be the paid-up capital according to the 



1 "Origin of Species," edition of 1859, p. 287. 



