122 THE BOOK OF NATURE STUDY 



through very different conditions at different times. The Chalk 

 must have been formed in deep water, the London Clay in the 

 delta of a great river, the Triassic Sandstones in a desert and 

 amongst salt lakes, the Wenlock Limestone in a coral sea, the 

 Coal Measures in a swampy forest. Such conditions could not 

 have been synchronous; they must have followed one another 

 successively. Therefore the physical history of a country is 

 written in the nature of its rocks, and by reading this history 

 we learn that a long and varied succession of events must have 

 followed one another to prepare its present condition, with all 

 its consequences of landscape, relief, outline, inhabitants, and 

 occupations. 



