THE GEOLOGICAL RECORD 205 



character of teeth in the jaws, although they have now typical 

 avian tails, wings, and skulls. Teleostean fishes and angiosperms 

 make their appearance, but the life is on the whole more closely 

 linked with that of the Mesozoic than of the Cainozoic rocks. 

 Sea urchins are common and brachiopods still prominent. The 

 rocks yield iron-stone, once much worked in the Weald, a fresh- 

 water limestone worked for marble, firestones, glass and filtering 

 sand, fullers' earth, brick clays, phosphatic nodules used for 

 manure, and flints used sometimes for building and road-making. 

 The Chalk is a very important source of lime for mortar and 

 cement, and it and the Greensands yield also considerable supplies 

 of underground water. The landscape consists of parallel scarps 

 and valleys like those of the Weald, and the Chalk Downs form 

 one of the most conspicuous features of southern and eastern 

 England. The soft chalk is capable of forming hill ground (Fig. 70), 

 partly because it is relatively harder than the clays above and 

 below it, and partly because most of the rain water is absorbed 

 readily by it and does not often form denuding streams on its 

 surface. Valleys in a chalk country are almost invariably dry. 



The Eocene System of rocks is confined to the London and 

 Hampshire Basins. The rocks are mainly clays, sands, and 

 shelly marls, deposited in the estuary of a tropical river. The 

 fossils are mainly marine, though fresh- water and estuarine bands 

 occur, and both animals and plants begin to show affinities with 

 forms still living, most of them in tropical latitudes. During 

 part of the Period, volcanoes became unusually active in many 

 parts of the world, and especially on the west coast of Scotland 

 and the north-east of Ireland. 



Brachiopods are no longer conspicuous, their place being 

 taken by lamellibranchs and great abundance of gastropods 

 (Fig. 74), which show affinities with those now living in the 

 Indian Ocean. Crinoids, sea urchins, and cephalopods are 

 much less conspicuous. Foraminifera are common, and some, 

 like nummulites, exceptionally large, and building whole masses 

 of limestone. The great profusion of Mesozoic reptiles dis- 

 appears, leaving only crocodiles, turtles, and snakes. Birds are 

 almost normal. The method of formation of the rocks has 

 allowed the preservation of numerous mammalia. Marsupials 



