SURVEY OE THE BRITISH ISLES FOR THE EPOCH JANUARY 1, 1886. 313 
surface are in such marked contrast, it may be open to question whether strong 
magnetic attraction in a district in which no crystalline rocks appear on the surface 
does not indicate not only crystalline hut basic crystalline rocks beneath it. 
However this may be, there are two regions of attraction which are not connected 
with basaltic rocks on the surface, at all events as the main cause of their 
peculiarities. 
One of these runs westw^ard from London to the South Wales CoaJ-field, and the 
directions of the disturbing forces in Wexford are such as would be caused if it crossed 
the Irish Channel. This extension is doubtful, but the line is most clearly marked 
right across England, and its general direction is such as to make it almost impossible 
to avoid the conclusion that it is connected with the palreozoic ridge, the existence of 
which, long ago predicted by Mr. Godwin Austen, has lieen jrroved by deep borings 
near London, and which is supposed to connect the Welsh and Belgian Coal-fields. 
If the palaeozoic rocks are nearer the surface here than elsewdrere, the cr^^stalline 
rocks may approach it also wfithin a moderate distance, and if they are susceptible to 
magnetisation the observed results would follow. The palaeozoic rocks are supposed 
to form basins, and if those beneath them have a similar outline, it would be possible 
to explain a centre of attraction such as the Reading peak. 
The last region of attraction runs from the Wash through south-east Yorkshire 
toward the Cumberland Lakes, and, as Professor Judd first pointed out to us, it 
includes the line to the north of the Humber, along which the oolitic and liassic 
strata thin out rapidly, and where, therefore, the crystalline rocks are probably 
suddenly brought much nearer to the surface. It is continued northward toward the 
igneous masses in Cumberland. 
The centre of attraction which apparently exists at Kells, in Ireland, is not suffi¬ 
ciently accounted for by the surface geology of the district in which it is placed, and 
we have not felt ourselves justified in representing it as connected with the Antrim 
basalt, as the fact that this connection requires further confirmation has been already 
pointed out. 
On the whole, then, we think we may assert that every region of magnetic 
attraction, with the possible exception of that near Kells, is marked either by the 
presence of basalt, or by some geological peculiarity which makes it possible or even 
probable that within it crystalline rocks, capable of affecting the magnet, are nearer 
the surface than elsewhere. This is possible as regards the line of fault marked l)y 
the Caledonian Canal, and probable as regards south-east Yorkshire and the soutlr of 
England. 
The former district is remarkable from the fact that it was far more strongly 
afiected by the earthquake of Lisbon than tlie rest of the British Isles, and this may, 
perhaps, indicate that it has special relations to the primary rocks, wdiich would 
account for its magnetic importance. 
MDCCCXC.—A. 2 S 
