106 
EXPLANATION OP PLATE 67. 
the sea-shore j this figure is intended to illustrate 
two causes of the production of Springs by descent 
of water from porous strata at higher levels ; the 
first, producing discharges in vallies of Denudation, 
along the line of junction of porous with imperme- 
able strata ; the other, by the interruption offered 
to descent of water by Faults that intersect the 
strata. 
The Hills A, C, are supposed to be formed of a 
permeable stratum a, a', a", resting on an imper- 
meable bed of Clay A, h', b". Between these two 
Hills is a Valley of Denudation, B. Towards the 
head of this Valley the junction of the penneable 
stratum a, a', with the Clay bed b, b' , produces a 
spring at the point S. ; here the intersection of 
these strata by the denudation of the valley affords 
a perennial issue to the Rain water, which falls 
upon the adjacent upland plain, and percolating 
downwai’ds to the bottom of the porous stratum a,d, 
accumulates therein until it is discharged by nume- 
rous springs, in positions similar to S,near the head 
and along the sides of the vallies which intersect 
the junction of the stratum a, a', with the stratum 
b, V . See V. I. p. 559.* 
The Hill C, represents the case of a spring pro- 
duced by a Fault, H. The Rain that falls upon 
this Hill between H, and D, descends through the 
porous stratum a", to the subjacent bed of Clay b". 
* The term Comhe, so common in the names of upland Villages, 
is usually applied to that uiiwatered portion of a valley, which forms 
its continuation beyond, and above the most elevated spring that issues 
into it; at this point, or spring head, the valley ends, and the Comte 
begins. The conveniences of water and shelter which these spring- 
heads aflbrd, have usually fixed the site of the highest villages that 
are planted around the margin of elevated plains. 
