AND LEICESTERSHIRE AND THEIR RELATIONS TO GEOLOOICAL STRUCTURE. 125 
The low susceptibility rules out such rocks as the clay-ironstones of the Coal 
Measures, also any licematite deposits or ferruginous dolomites or basalt lavas, such 
as might occur in the Carboniferous Limestone if present underground. Similarly, 
it would rule out the various intrusive rocks— granophyres and porphyvoids —which 
occur in the Charnian, also the camptonites which might be present in any Cambrian 
rocks if such are developed in the district. 
Effect of Possible Granite Intrusions. —Apart from the dolerites, the only rocks 
of a susceptibility approaching that demanded by the magnitude of the disturbances, 
are the Mount Sorrel granite and associated rocks. The value ranged from 60 to 
130 X 10"” for the typical rock to as high as 181 x 10“® for the included basic patches 
or “ heathen,” which are often very abundant. The latter figure is comparable to 
that given by dolerites, and the question arises whether the disturbances noted can 
be ascribed to the buried masses of granite rather than to dolerites. 
Unfortunately, there is no observation station within four miles of the visible 
granites, so that we do not know whether the Mount Sorrel mass itself exerts 
any disturbing influence. It is suggestive, however, that the large disturbance at 
Loughborough, the station nearest the granite, shows no connexion with the visible 
granite four miles south-east, but associates itself with the Rempstone centre of 
disturbance, that is, the Rempstone Fault, four miles north-east of Loughborough. 
This would seem to tell against the granite exerting any great influence, unless, 
indeed, there should be a larger or more powerful granite mass under Rempstone. 
Again, there is an almost complete lack of geological evidence either for or against 
such an hypothesis. The Mount Sorrel granite is, so far as surface exposures go, an 
isolated mass. But it has been shown (p. 102) that in view of its petrological 
character, and probable age, no similar granite could be expected to occur in 
Carboniferous or newer rocks, although similar granites might well occur in rocks 
older than the Carboniferous. Thus the Mount Sorrel intrusion may not in reality 
be as isolated as it appears, and there may be other granites in the district that 
could give rise to disturbances. 
The Charnian rocks, with which the granite is associated, continue underground 
under a comparatively shallow cover along their direction of strike, that is, to the 
south-east. But to the north-east the irregular plane of junction between them and 
the overlying Trias usually dips steeply. Therefore any Charnian rocks would most 
likely lie very deep under Rempstone, four miles north-east of the outmost Charnian 
strike-line, and possibly still deeper under Melton Mowbray, 10 miles from the line. 
On the other hand. Carboniferous rocks, with possibly associated dolerites, almost 
certainly intervene at lesser depths, as previously described. 
Dr. W ALKER writes : “ Since the granites may attain a susceptibility of nearly 
200x 10"®, they become a possible source for disturbances measured by 200y, 
as at Rempstone. Their susceptibility, however, according to the rule (p, 82), 
represents about the minimum value necessary to cause disturbances of the 
