i893. THE UNDERGROUND WASTE OF THE LAND. 127 



to this undermining action of land-springs, and the consequent 

 disruption of the strata. 



Thus the level of the land may be lowered by springs carrying 

 away sand, and also by their eroding channels in the clays over which 

 they take an underground course. We may also discern a way in 

 which outliers have been produced, many of which, like Glastonbury 

 Tor and Brent Knoll in Somersetshire, appear to owe their preserva- 

 tion to a gentle, basin-shaped structure in the arrangement of their 

 strata, Mr. T. V. Holmes has pointed out that some of the out- 

 liers of Bagshot Beds in Essex probably owe their existence to 

 similar causes. 



Minor instances of erosion beneath clay may sometimes be 

 noticed. Thus in seasons of drought a superficial layer of clay may 

 contain deep cracks, and bands of limestone three or four feet from 

 the surface may bear evidence of erosion by carbonated water. Joints 

 in limestone that have been widened into fissures by chemical erosion 

 are often filled up with clayey material from beds above, and when 

 the rocks are much fissured and eroded, small dislocations sometimes 

 occur that produce a kind of faulting which does not affect the 

 underlying strata. In these ways the level of the land is slightly 

 lowered in many places. 



Lyell (i) has referred to the depression of " submarine forests" 

 by the drainage of peaty soils on the removal of a seaward barrier 

 that formerly prevented the escape of the waters. His attention was 

 drawn to the subject by observations published by the Rev. Dr. 

 Fleming; and Lyell applied the explanation to a case at Bourne- 

 mouth. There "the sea, in its progressive encroachments, even- 

 tually laid bare, at low water, the foundations of this marshy ground; 

 in this case, much of the sand, of which these foundations were com- 

 posed, might have been washed out by the rapid descent of the fresh 

 water through them, at the fall of the tide." 



John Cunningham (2), as pointed out by Mr. G. H. Morton (6), 

 gave a somewhat similar explanation of the submarine forest of 

 Leasowe ; and very recently Mr. William Shone (5) has drawn atten- 

 tion to the subject in a paper referring to the same district. It must 

 be confessed that these suggestions have yet to be substantiated. 



Nevertheless, the subject of subterranean erosion by mechanical 

 agency is one to which more attention may profitably be directed. 

 The observations here recorded tend to show that the amount of 

 erosion, whether mechanical or chemical, great as it must be, is 

 hardly perceptible except locally. Our main features are of great 

 antiquity, and, although the present forms of escarpments are due to 

 subaerial agents, yet but a small amount of rock (a mere "notch ") 

 has been removed in this way compared with original extent of the 

 strata. Into that particular subject it would, however, be undesirable 

 now to enter, my object being simply to draw further attention 

 to the question of underground erosion; and to point out how it is 



