658 
MR. A. W. RtiCKER ARD DR. T. E. THORPE OX A MAGNETIC 
not correspond with any surface indications. A slightly marked line, which is 
probably connected with this, runs north-east from Lichfield to Nottingham, 
passing through the patch of older rocks which occurs to the nortb of Charnwood 
Forest. 
To the east of Pteading the more southerly of the two ridge lines coincides roughly 
with the line of the Palseozoic ridge, but it is rather to the south of the points in which 
the oldest rocks probably approach nearest to the surface. The more northerly line 
passes through Ware, near which Silurian rocks have been proved. 
In the north of England the magnet is attracted to a line which roughly follows the 
axis of greatest o-eological elevation from the Lake District to Harrogate, and thence 
southwards through Derbyshire. A branch traverses the Lancashire Coal Field, which 
projects like a promontory'among later formations. 
This concludes the evidence that there is a certain though somewhat loose connec¬ 
tion between ridge lines in England and regions of upheaval of the older rocks. 
The Derbj^shire and the Yorkshire magnetic ridges are obviously prolonged under 
the new'er strata in the East Midland and Eastern Counties. The latter line 
especially passes close to Market Weighton, where the Jurassic rocks thin out, and 
which was recommended as a station by Professor Judd on account of the probability 
of the older rocks approaching the surface there. In South-East Lincolnshire folds in 
the new strata have recentlv been discovered, wdiich run parallel to our ridge line, and 
may be connected with more deeply-seated undulations. 
In Scotland the magnetic lines appear to be chiefly associated with the basaltic 
masses and the faults. These have been already discussed. 
In Ireland a ridge line is associated with a succession of Silurian masses, which lie 
between newer rocks, and are marked by the Gal tee, Silvermine, and Slieve Bloom 
Mountains respectively. 
It is connected with a slightly marked ridge line, which appears to be a continuation 
of the Palmozoic ridge, and with others which run to the igneous rocks of Connemara 
and of South Down. From Connemara the ridge is continued north-east parallel to 
the Silurian ridges and to the faults which occur in this part of the country. 
On the vvhole then it appears that the connection between the magnetic ridge 
lines and the geological conformation of the country, though in some cases clearly 
suggested, is only such as would follow if the magnetic eftects were due to deep- 
seated folds in the magnetic rocks, which are not always directl}^ connected with the 
arrangement of the surface rocks. 
The general results may be summed up as follows :— 
(1.) Theory leads us to expect, and experiment shows that dykes and thin basaltic 
sheets produce no measurable Disturbances at distances which are small multiples of 
their thickness. 
(2.) Theory leads us to expect, and experiment shows that masses of trap rock, a 
