296 PHYSIOGRAPHY. [chap. 



The study of the fossils contained in the strata of the 

 Thames basin is not only of essential importance in proving 

 the changes which have occurred in its physical geography, 

 but it brings to light other remarkable facts in the history of 

 the region. It has been seen that animals, which now live in 

 both colder and warmer climates than those of the Thames 

 basin, are found associated together in the drifts ; and that, 

 in the older rocks, the remains are such as resemble the 

 present inhabitants of warmer climates. But, while the great 

 majority of the animals and plants of the drifts are identical 

 with, or very similar to, those which now live somewhere or 

 other; the inhabitants of the world in former ages become less 

 and less like those which now exist, as we go back in time. 

 Thus, although in their general character, the animal 

 remains of the London clay resemble those of animals now 

 living in hot climates, it is only a small percentage which are 

 identical with living forms ; while the rest have altogether 

 vanished and become extinct. In the chalk, this feature is 

 still more marked. Of the many thousand beautifully-pre- 

 served kinds of animal remains which have been obtained 

 from that formation, only a very few of the lower forms are 

 identical with species now living. Hence, notwithstanding 

 the similarity of the chalk to the Globigerina-oioze, the 

 remains imbedded in the former at once distinguish it from 

 the modern deposit. 



The common-sense reasoning which deduced from the 

 facts of the Cannon Street section, the conclusion that a 

 people, having the language and customs of the ancient 

 Romans, preceded the English inhabitants of that locality, 

 applied to the subjacent strata, has permitted no doubt that, 

 at some period before the Roman occupation, the Thames 

 valley was the haunt of savages armed with flint weapons \ 



