chap. viii. Formation of Sea-Cliffs. 



229 



islands, in which the gentle inclination of the lava- 

 streams indicates the former extension of the land, a 

 difficulty often occurred to me, namely, how the strata 

 could possibly have been removed by the action of the 

 sea at a considerable depth beneath its surface. The 

 following section, which represents the general form of 

 the land on the northern and leeward side of St. Helena 

 (taken from Mr. Seal's large model and various measure- 

 ments), and of the bottom of the adjoining sea (taken 

 chiefly from Captain Austin's survey and some old 

 charts), will show the nature of this difficulty : — 



No. 21. 

 Section of Coast Cliffs and Bottom of Sea, off the Island of St. Helena. 



1,600 feet 

 above sea. 



SO fath. 



100 fa. 250 fa. 



Level of sea. 



Bottom rocky 

 only to a depth of 

 five or six fathoms. 



Mud and sand. 



Vertical and horizontal scale, two inches to a nautical mile. The point marked 

 1,600 feet is at the foot of High Knoll ; point marked 510 feet is on the edge of 

 Ladder Hill. The strata consist of basaltic streams. 



If, as seems probable, the basaltic streams were 

 originally prolonged with nearly their present inclina- 

 tion, they must, as shown by the dotted line in the 

 section, once have extended at least to a point, now 

 covered by the sea to a depth of nearly thirty fathoms : 

 but I have every reason to believe they extended con- 

 siderably farther, for the inclination of the streams is 

 less near the coast than farther inland. It should also 

 be observed, that other sections on the coast of this 

 island would have given far more striking results, but 

 I had not the exact measurements ; thus, on the wind- 

 ward side, the cliffs are about 2,000 feet in height and 



