664 THE POPULAR SCIENCE MONTHLY. 



the upheavals and subsidence of strata which characterize the earth's 

 crust were produced suddenly, and by violent agencies, the school 

 to which he belonged were little likely to attempt to fix a date for 

 the creation of the world. To their minds the facts of geology gave 

 no evidence as to time. It is, therefore, to Sir Charles Lyell and his 

 followers that we must turn for an estimate of duration drawn from 

 the " testimony of the rocks." 



It is impossible to deny that periods of very vast duration must 

 have elapsed while the changes took place of which we see the traces. 

 If, for instance, we search below the sand on English shores, we rind, 

 perhaps, a bed of earth with shells and bones; under that, a bed of 

 peat ; under that, one of blue silt ; under that, a buried forest, with 

 the trees upright and rooted ; under that, another layer of blue silt, 

 full of roots and vegetable fibre; perhaps, under that, again, another 

 old land-surface, with trees again growing in it ; and, under all, the 

 main bottom clay of the district. In any place where bowlder clay 

 crops out at the surface in Cheshire or Lancashire, along Leith shore 

 near Edinburgh, or along the coast of Scarborough it will be found 

 stuffed full of bits of different kinds of stone, the great majority of 

 which have nothing to do with the rock on which the clay happens to 

 lie, but have come from places many miles away. On examining the 

 pebbles, they will prove to be rounded, scratched, and grooved, in 

 such fashion as to show that at some period they have been subjected 

 to a grinding force of immense violence. Among the pebbles in the 

 clay, and on plains far away from mountains, are found great rocks 

 of many tons in weight. They were carried on the backs of icebergs, 

 which, at some time, covered the now tempex-ate regions of the earth, 

 and were dropped by the melting ice either in the shape of pebbles, 

 as moraines of ancient glaciers, or as bowlders stranded when the ice- 

 bergs melted in the lowlands. 



Such evidence points to vast periods of more than arctic winter, 

 which must have endured for many thousand years. But in close 

 juxtaposition with these glacial shells and pebbles lie remains which 

 tell of tropical climates that alternated with the dreary ages of ice. 

 Fossil plants and the remains of animals prove that all Northern Eu- 

 rope was once warmer than it is now ; that England bore the flora 

 and fauna of the torrid zones. Underneath London there lies four or 

 five hundred feet of clay. It is not ice clay ; it belongs to a later 

 geological formation, and was, in fact, the delta of a great tropical 

 river. The shells in this clay are tropical nautili, cones, fruits, and 

 seeds of nipa palms, now found only at Indian river-mouths ; anona- 

 seeds, gourd-seeds, acacia fruits ; the bones, too, of crocodiles and 

 turtles ; of large mammals allied to the Indian tapir, and the water- 

 hog of the Cape. All this shows that there was once, where London 

 st-mds, a tropical climate, and a tropic river running into the sea. 

 "We find in it the remains of animals w r hich existed before the Ice a<re. 



