ON A CHALK HILL 221 



are recent ; in the earlier tertiary deposits we find the 

 proportion of recent shells gradually falling to 50 per cent., 

 10 per cent, and 3 per cent. But in the chalk all the 

 mollusca are extinct, and we have to get very low down in 

 the animal kingdom, to infusorians and Foraminifera, before 

 we can find species identical with those which still survive. 



The lapse of time since the chalk was laid down may 

 be roughly estimated in another way. Europe has been 

 reconstructed since the chalk-time. During the formation 

 of the chalk a great sea stretched from east to west across 

 what is now Central Europe, extending from the British 

 Islands to Sweden, France, Germany and Russia. The 

 Alps, Pyrenees and Carpathians did not as yet exist, 

 for we know that a thick bed of limestone, younger than 

 the chalk, runs through all these mountain-ranges. When 

 we have said that the chalk is older than all existing 

 species of animals except the very lowest, and that it is 

 older than Europe, we have said all that can be demon- 

 strated concerning its age. 



What might we expect to have seen if we could have 

 stood on some hill-side in these latitudes while the chalk 

 was being laid down in the neighbouring seas ? The 

 reader must not look for any description such as Hugh 

 Miller used to shape in his eloquent words when a good 

 occasion offered ; next to nothing is known of the land- 

 life of the chalk-period. When we have said that there 

 were flying reptiles, great reptiles that browsed upon 

 foliage, toothed birds (in America if not in England), some 

 insects, some conifers and some ferns, we are almost at 

 the end of our information. Few indications of land-life 

 are indeed to be expected in rocks deposited beneath the 

 sea, and as the secondary formations are nearly all marine, 

 it is not surprising that from the coal-measure time to 

 the early tertiary period our knowledge of the course of 

 life on the land should be almost a blank. Of the reptiles, 

 fishes, shells, sea-urchins, starfishes and corals of the 

 chalk-sea much is known, but the forests of the secondary 



