THE PROBABLE AGE OF THE WORLD. 665 



The mammoth, or woolly elephant, the woolly rhinoceros, the cave- 

 lion, the cave-hear, the reindeer, and the musk-ox, inhabited Britain 

 till the ice drove them south. When the climate became tolerable 

 again, the mammoth and rhinoceros, the bison and the lion, reoccupied 

 our lowlands ; and the hippopotamus from Africa and Spain wandered 

 over the plains where now the English Channel flows, and pastured 

 side by side with animals which have long since retreated to Norway 

 and Canada. 



When the ages necessary for all these changes is allowed for, we 

 have not, even yet, got beyond the latest period into which the his- 

 tory of the globe has been divided. Under the tertiary deposits lies 

 the chalk, a thousand feet in thickness, which is composed of the shells 

 of minute animals, which must have been deposited age after age at 

 the bottom of a deep and still ocean, far out of reach of winds, tides, 

 or cnrrents. Recent dredgings in ocean-depths have proved beyond 

 a doubt that the greater part of the Atlantic Sea floor is now being 

 covered by a similar deposit. It must have taken ages to form, and, 

 if the geologists are right in their estimate of the slow rate of up- 

 heaval, many more ages to become elevated above the ocean-bed 

 where it lay. Not only once, but many times, the chalk was alter- 

 nately above and beneath the waves. It is separated by comparative- 

 ly thin and partial deposits of sand and clays, which show that it has 

 been at many different points in succession a sea-shore cliff. The 

 chalk is not flat, as it must have been at the sea-bottom; it is eaten 

 out into holes by the erosion of the sea-waves, and upon it lie flints, 

 beds of shore-shingle, beds of oysters lying as they grew, water-shells 

 standing as they lived, and the remains of trees. Yet, again, there 

 lie upon the chalk sands, such as those of Aldershot and Farnham, 

 containing in their lower strata remains of tropical life, which disap- 

 peared as the climate became gradually colder and colder, and the age 

 of ice once more set in. Everywhere about the Ascot Moors the sands 

 have been ploughed by the shore-ice in winter, as they lay awash in 

 the shallow sea, and over them is spread in many places a thin sheet 

 of ice-borne gravel. All this happened between the date of the bowl- 

 der clay and that of the New Red Sandstone on which it rests. 



We need not follow the geologist through the lower systems 

 which overlie the metamorphic rock. The Oolite contains remains of 

 plants and animals now extinct, the most remarkable being huge rep- 

 tiles; the Triassic has fossils like the Oolite ; and the Permian has 

 remains like those in the coal on which it rests. Then follow the coal- 

 measures, the fossil remnants of tropical vegetation ; the Old Red 

 Sandstone, with fossils principally of fishes and shells ; the Silurian, 

 in which are found the earliest forms of life ; and, lastly, the hard and 

 crystalline rocks, devoid of fossils, which are supposed to be the earli- 

 est constituent mass of our planet. 



Sir Charles Lyell and his followers allege that the rate at which 



