ae 
parallel fissures and faites fractures, similar to those in the 
Weald of Kent and Sussex. In the mining districts of Cornwall, 
particularly near Redruth, these rents and fissures are known in all 
their various and curious details, from their having been excavated 
in search of the metallic ores which they contain. The main direc- 
tion of these fissures being east and west, they are intersected, like 
those in the south-east of England, by transverse fractures or cross 
courses, running nearly north and south. Both these systems in 
- Cornwall obviously result from the same mechanical laws which 
have not only caused transverse fractures to intersect the longitudi- 
nal lines of elevation, in the districts of the Weald and Derbyshire, ; 
where Mr. Hopkins has demonstrated their accordance with the the- 
oretical laws of physical induction ; but will be found to have affected 
every mountain chain produced by angular elevation upon the sur- 
face of the globe. 
_ Inthe Annals of Philosophy, 1821, p.453, I published a Memoir on 
the Structure of the Alps, in which it was shown that all the rivers 
which descend on the north side of this greatest European moun- 
tain chain, escape from longitudinal valleys parallel to the general 
axis of elevation and to the.escarpments of the elevated strata, by a 
_ series of gorges transversely intersecting these escarpments ; in the 
same manner as the four gorges, that intersect the Chalk escarp- 
ment of the South Downs, give outlet to four rivers formed in lon- 
gitudinal valleys on the south side of the central axis of the 
Wealden elevation, namely, the Arun, Adur, Ouse and Cuckmere 
rivers; whilst five gorges in the escarpments of the North Downs 
give exit to five rivers formed in longitudinal valleys on the north 
side of the same central axis of the Weald, namely, the Wey, the 
Mole, the Darent, the Medway, and the Stour. 
An objection has been sometimes raised to the theory which at- 
tributes the existing position of inclined strata to elevation, grounded 
onan assumption that the same relative positions of the strata in moun- 
tains and the valleys adjacent to them may have been caused by the 
subsidence of the lower parts of the strata into the basins, as by the 
elevation of those portions which now occupy the highest place ; but 
these objections are overruled by mechanical and mathematical 
reasons, arising from observation of the relative positions of the dis- 
located strata on each side of the “ upcast dykes” or faults that 
run parallel to these assumed lines of elevation; namely, that the 
dislocated strata, in almost all cases, occupy the place which an up- 
ward movement would have given to them respectively on each 
side of the fault, and which they could not have received from a 
downward movement under any process of depression*. 
* It is due to the memory of Mr. Farey, the cotemporary and fellow- 
labourer of Mr. Wm. Smith, that we should here notice the fact of his 
having many years ago presented to this Society an unpublished section 
across the Weald of Sussex, along the road from London to Brighton, to 
which due:credit. was not then attached. In this section, together with 
the general direction of the component strata of the district, as given in 
the sections of Mr. Mantell and Dr. Fitton, he introduces a series of 
