THE HISTORY OF LIFE 201 



And still more remarkable, these organic layers or 

 strata become in places altered into a compact, 

 crystalline, marble-like structure, which can hardly be 

 distinguishable from Primary or the older metamorphic 

 rocks. With this evidence before us, the mind tends 

 to the idea that the materials of some igneous rocks were 

 altered sedimentary rocks, that is, that the materials 

 of the igneous rocks were originally deposited in water 

 and subsequently altered by complete melting. 



The plants which existed in the clay, which is so 

 well developed in the neighbourhood of London, 

 known as the London Clay, indicate that the climate 

 was, during its deposition, a warm one. Palms and 

 cacti flourished when the clay was formed. But as 

 we trace subsequent layers, we find that the plant life 

 approaches the English plant life of to-day. 8hell-fish 

 existed of the same types as now live in the Avarmer 

 seas of our globe. Tortoises, turtles, crocodiles, and sea- 

 snakes lived in the rivers and seas which existed where 

 England and Europe are now dry land., Birds lived 

 in variety, and forms, allied to the buzzard, osprey, 

 hawk, quail, pelican, and other existing species, then 

 lived. In the lower formations are found primitive 

 animal-eating or carnivorous mammals. Tapir-like 

 animals, and mammals living on insects, now appear. 

 And also the earliest representatives of the more ad- 

 vanced form of mammal likewise appear the lemuroid 

 monkeys are created. Creatures between the tapir and 

 the horse spring into existence, having three toes on 

 each foot, and they are regarded as the ancestors of 

 the horse. The remains of numerous hog-like animals, 

 mingled with herds of hornless forms of deer and 

 antelopes, are found in these strata. Animals re- 



