SURVEY OF THE BRITISH ISLES FOR THE EPOCH JANUARY I, 1891. 637 
fact that the district is close to the coast makes it difficult to determine its 
characteristics in detail. 
The most probable hypothesis appears-to be that the Saltee Islands are on the 
intersection of two ridge lines. The most interesting of these is that which is traced 
as a secondary ridge from Mountrath to the Saltees. 
Its direction strongly suggests its connection with the great ridge line which runs 
across the South of England and Wales and enters St. George’s Channel near 
St. David’s Head. 
No. 21 .—Fragmentary Coast Districts. 
Four portions of Ireland are cut olf magnetically from the rest by valley lines, but, 
as they are also bounded by the sea, they are evidently only fragments of magnetic 
regions, and do not present features of any special interest. One of these is to the 
north of Donegal Bay. Another includes the county of Kerry, with parts of Cork, 
Limerick and Clare. In both of these the centre of attraction appears to bo under 
the sea. 
A third small District surrounds Bantry Bay. A ridge line runs through it, which 
is connected with that whicli has already been traced from Nenagh to Bandon. 
The fourth District surrounds the town of Wicklow. 
It will be referred to hereafter in the discussion on the connection between the 
magnetic and geological characteristics of this part of Ireland. 
On the Relation between the Magnetic and Geological Constitution of 
THE United Kingdom. 
Up to this point we have purposely con lined ourselves exclusively to the discussion 
of the results of our magnetic observations. The arguments for and against the 
conclusions at which we have arrived have been set forth, and we have distinguished, 
as far as possible, between views which we believe to be indisputable and those which 
must be regarded as only more or less probable. 
In discussing the relations between our magnetic ridge and valley lines, and the 
geological constitution of the districts through which they run, we do not propose to 
balance again the facts by which we have been led to the opinions represented in 
Map 13. We shall assume—as we think we are entitled to assume—that they are 
in the main correct, and we shall compare them with the conclusions of geologists. 
One of us has already discussed the question as to how far the Disturbances we have 
observed are of the same order of magnitude as those which would be produced by 
large underground masses of rock of the magnetic susceptihility of the basalts and 
gabbros which occur on the surface. (‘Proc. Roy. Soc.,’ 1890, vol. 48, pp. 505-535.) 
The general conclusion arrived at was that such a cause would be adequate to produce 
the observed effects. One point, however, which was not specially insisted on, 
deserves further elucidation. 
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