158 THE GEOLOGIST. 



tell US too of a gradual refrigeration of our planet, and refer many 

 problems of former temperature to the ancient higher internal incan- 

 descence of our planet. Measure off on a roll the successive masses 

 of rock-strata which we know by their superposition to be true in i- 

 cations of geological time, on a scale of IJ inch to a thousand feet of 

 vertical thickness, and your diagram will reach to a length of nearly 

 nine feet. 



Over the uppermost of these add a segment to represent recent 

 deposits ; it will scarcely be the eighth of an inch in thickness. Yet 

 four thousand years at least have intervened since the parents of the 

 human race trod the verdant floor of beauteous Eden. Take the 

 next in order, the latest Tertiary age — the age of glacial drifts and 

 icebergs, and a quarter of an inch will overlap the segment you have 

 drawn. And yet for thirty thousand years at least the foaming cataract 

 of Niagara has been cutting throngh the raised and consolidated strata 

 of that vast age, for vast it must have been when whole species of 

 maritime mollusca migrated many geographical degrees from their 

 ancestral haunts to seek out warmer climes ; when whole continental 

 tracts were raised into the regions of perpetual snow ; and again, the 

 uplifted lands subsiding to their ancient levels, their shores were once 

 more inhabited by the returned posterity of the out-driven shell-fish. 

 Take the next segment of the rock- formations, and the caves disgorge 

 the bones of hundreds of extinct pachyderms and ruminants. Com- 

 pute the cubic space of the fleshly bulk of the collective carcasses of 

 those exhumed by inquiring man alone, and their volume far surpasses 

 the capacity of the cave to contain them ; and yet for hundreds 

 disinterred, thousands remain behind. Take the next age, and two 

 thousand feet of sediment tell of still more extensive changes and still 

 more extended time ; and the next, and the next j and greater and 

 greater becomes the thickness of the stony volumes of the earth s 

 history, until in the coal-measures we have 15,000 feet and more of 

 instructing leaves, and in the Silurian and the "bottom-rocks" 

 25,000 and 2G,000 feet of evidential records. 



These too are only the records of the periods of active deposit of 

 sediment, and the minimum even of that. No indication is here of 

 the periods (equally great, or greater) of cessation, nor of the far sur- 

 passing periods of re-generation and re-formation. The greatest 



