258 SUBTERRANEAN EROSION, 
drainage of the land in the rear of the section escaped into the 
River Mersey. The underground water must accumulate most 
in the centre of each rock-basin, and consequently exert its 
greatest force in the lower portions of each hollow, with the 
result that the mingled Peat and Forest-beds would increase in 
thickness towards the centre of each rock-basin until submerged 
and buried under the Blue Clay which divides the Upper and 
Lower Beds. 
In, brief, the stratigraphical history of this most interesting 
section appears to me to be as follows :—The Lower Forest-bed 
flourished upon Glacial Drift very little above the water-level of 
the district. By subterranean erosion the level was gradually 
lowered between the points X! and X?, X° and X*, X® and X*, 
X' and Y, until the site of the forest became a peat-morass, 
which was eventually covered with Blue Clay. The time came 
when the drainage was interrupted and subterranean erosion 
ceased ; then the Upper Forest-bed spread out from the points 
of continuous growth (X! to X’) across each rock-basin. It 
flourished until the cause of the interrupted drainage was 
removed, when subterranean erosion again became active, and 
the Upper Forest-bed sank below the water level, while peat- 
mosses grew on its site, until in turn they were buried under 
tidal silt—the rate of subterranean erosion at present being 
more rapid than the increase of the thickness of the peat by 
growth. 
The principal characteristic of subterranean erosion is /a/eral 
subsidence. Jn/ermitient action follows as a natural consequence. 
This is especially the case when an zmpervious bed rests upon a 
pervious one, aS in fig. 2. The liability of subterranean erosion 
to be interrupted along any inclined plane of underground 
drainage, is, in my opinion, the cause of the bifurcation of the 
Peat and Forest-beds; while the thinning-out of the deposits 
which separate them into Upper and Lower towards each point 
of bifurcation shows that the subsidence in each case was 
gradual and lateral. ; 
Mr. T. Metrtarp READE published in the “ Proceedings of 
the Geological Society of Liverpool,” for 1871-72,* a number of 
very valuable sections of the post-Glacial deposits of Lancashire 
and Cheshire, from which the general tendency of Peat and 
Forest-beds to subside laterally is very obvious. 
After the publication of my paper on ‘‘Subterranean Erosion,” 
in the Quarterly Journal of the Geological Society, Mr. G. H. 
Morton, F.G.S.,+ called attention to the fact that the late Mr. 
John Cunningham, F.G.S., in a paper read before the British 
Association, in 1854, ‘“‘On the Submarine Forest, Leasowe,” had 
come to very similar conclusions to myself, with regard to 
* Op. cit. p. 36 et seg. and plates ii.-iv. 
+ Geological Magazine, September, 1892. 
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