656 
MR. A. W. RtrCKER AND DR. T. E. THORPE ON A MAGNETIC 
The Horizontal Disturbing Forces in such a case will not be directed to the fault, 
but to the centre of the mass of Avhich it makes the boundary. 
According to Sir Aechibald Geikie, however (‘Encycl. Brit.,’ Ed. TX., vol. 10, 
p. 261), a fault or dislocation is nearly always inclined to the vertical. 
If the basaltic slab, which is assumed to underlie it, were not horizontal, the effects 
of the fault itself would be interfered Avith and marked by the Disturbances due to 
the approach of the mass towards the surface. 
There is, therefore, no d priori reason for supjDOsing that a fault must coincide with 
a line of attraction. 
If it does, it will be rather a proof of a favourable conformation of hidden magnetic 
rocks than an illustration of a general principle. Thus, two stations at BeAvdley on 
either side of the well-known fault, vdiich runs from that place toAvards Malvern, do 
not appear to be affected by it. 
In Scotland and the North of Ireland, however, some of the magnetic ridge 
lines, if not coincident with, are for some distance parallel to important faults. 
This is true of the Great Glen (Caledonian Canal), of the fault which crosses Scotland 
from the Clyde to Stonehavmn,* and of the fault AAdiich runs south-Avest from Antrim. 
These facts are sufficiently illustrated on Map 14. 
The magnetic observations tend to shoAv that the fault line of the Great Glen is 
prolonged northwards, but, on the other hand, the extension of the fault southwards 
by Loch SAvilly to Donegal Bay is not indicated b}^ the magnet, or is masked by the 
neighbourhood of the A ntrim and Donegal basic rocks. 
A magnetic ridge line runs close to the South Highland fault for about 60 miles. 
It appears, hoAvever, to cross it near its northern boundary and does not follow its 
prolongallon south-Avest toAvards Donegal Bay. 
'I’he GalloAvay ridge line runs for some distance nearly parallel to, though at an 
average distance of some 20 miles from, the fault Avhich bounds the Mid-Scotland 
District on the south. 
For the rest, there does not seem to be any Amry close connection between the 
geology of Scotland and the other magnetic ridge lines in that country. 
Regions of Upheaval. 
If it be true that magnetic ridge lines sometimes indicate the physical ridge lines 
of underground magnetic masses, it seems probaffie that there Avould be a connection 
between them, and an anticlinal arrangement of the surface strata. It is eA'ident, 
however, that in this case, also, it is difficult to decide upon AAdiat Ave ought d priori 
to expect. 
No one, whose knowledge of the geology of the London basin aaxis confined to the 
surface only, Avould suspect the existence of the Palaeozoic ridge upon AAdiich it rests. 
It is quite possible that similar elevations of the assumed deep-lying magnetic rocks 
* This fact lias been established by our later observations. (See “ 1890 Memoir,” p. 318.) 
