CHRONOLOGICAL SEQUENCE. 65 



Order of superposition. — Such is the chrono- 

 logical sequence of the formations of the south- 

 east of England; in other words, these several 

 groups of marine and freshwater sediments, have 

 been deposited in the following order: — 



1st. The Wealden : the delta of a river, composed of the spoils 

 of a vast continent, of which no other vestiges remain. These 

 strata rest upon a marine formation called the Oolite, but which 

 does not come within the scope of our present observations. 



2dly. The Chalk : the bed of an ocean of great extent, deposited 

 upon the Wealden. 



3dly. The Tertiary Eocene Formation : accumulated in de- 

 pressions or basins on the surface of the Chalk.* 



Now, as each of these formations is many hun- 

 dred feet in thickness, it follows that the inferior 

 strata would for ever have been concealed from 

 observation, had the original order of super- 

 position remained undisturbed. But not only 

 portions of each of the upper series appear on the 

 surface, but even the lowermost deposits form an 

 extensive tract of country which is diversified by 

 hills and valleys, and constitutes one of the richest 

 agricultural provinces of the British Isles. This 

 distribution of the strata has originated from the 

 displacements occasioned by those disturbing forces 

 which elevated above the waters the ancient ocean 



* With the view of simplifying the subject, the Drift, or superficial alluvial 

 deposits, will not be especially alluded to in these excursions. 



