I50 Till: STORY OF THE EARTH. 



CHAPTER XIX. 



CHALK. 



The superposition of the chalk upon the 

 Upper Greensand, and the rocks which repre- 

 sent it, was the consequence of a rapid depres- 

 sion of old continental land from which the sedi- 

 ments had been denuded which built up the lower 

 cretaceous beds. Land did not entirely disappear 

 at once. There are a few places in Europe in 

 which the cretaceous flora is met with, such as 

 Aix-la-Chapelie, Ilalden in Westphalia, Quedlin- 

 burg and Blankenburg in the Harz, Molletin in 

 Moravia, and Niederschoena in Saxony. The 

 fossil plant-life found in these localities differs 

 a little, but includes similar types to those in 

 the cretaceous rocks of Greenland, and North 

 America. At Aix, the cretaceous basin consists 

 of sands and sandstones about 300 feet thick, 

 which rest upon the old primary rock which had 

 been a land surface. The sands have been re- 

 garded as of the age of the Upper Chalk, though 

 they contain some shells of the age of the Upper 

 Greensand. 



The chalk abounds in scattered fragments of 

 ancient crystalline rocks in its lower part. In 

 some localities in the south-east of England its 

 lower bedfl contain enough clay to give it an 

 aluminous odour; while, in the west of England, 



its lower beds frequently contain grains of quartz. 



.\iinity to land is indicated almost as definitely 

 by the preservation of branches of SeqtiOU$ % in the 

 lower chalk of ( 'ambridgeshire, and all through 

 the chalk period large timber trees are found 



