62 THE WONDERS OF GEOLOGY. Lect. I. 



Here we have a depression (or basin, as it is termed by 

 geologists) of chalk strata, partially filled up by layers of 



Chalk 



Ead. West. 



Lign. 7. — Section across Lewes Levels.* 



A. A. Silt, with river shells ; B. B. Clay, with river and marine shells; C. C. Deposit 

 with marine shells only. 



indurated mud or silt, the surface of which is clothed with 

 verdure ; the bed of the river (i) is situated near the 

 eastern chalk cliffs. By numerous sinkings through the 

 soil, carried from the surface down to the chalk bottom, 

 and the depth of which varied from fifteen to thirty feet, 

 the deposits have been ascertained to be as follow : — 



1. Bog-earth and peat, about five feet in thickness : formed of 

 decayed twigs and leaves of hazel, oak, birch, &c. inclosing 

 trunks of large trees. 



% (a. a.) — Blue clay, or indurated mud, containing several species 

 of fresh-water shells, like those which now inhabit the river and 

 ditches; with numerous indusice, or cases of the larvae of a 

 species of May-fly (phryganece) commonly termed caddis-worms. 

 Bones of horses and deer have been found in the lower part of 

 this bed. 



* A geological section represents the internal structure of the earth 

 on any given line, in a vertical direction ; and is either, 1, natural, as 

 seen in cliffs, precipices, &c; 2, artificial, as in quarries, tunnels, and 

 other excavations ; or, 3, theoretical, when constructed from a com- 

 bination of observations on the position of the strata in various 

 distant localities. 



