Reports & Proceedings — Geological Society of London. 335 



later movement being post-Triassic. Accordingly, it is probable 

 that the small dislocations in the Mesozoic rocks indicate the 

 presence of important faults in the underlying Palseozoic. 



The faults can only give rise to magnetic disturbances if they are 

 associated with rocks of high magnetic susceptibility. It is known 

 from deep borings that tlie concealed coalfield of JS'ottinghamshire 

 extends into Leicestershire, but how far is not known. Deep 

 borings have proved that intrusions of dolerite occur in the Coal- 

 measures at several localities in the south-eastern portion of the 

 concealed coalfield and always, so far as observed, in the immediate 

 vicinity of faults. It has been established that dolerites may exert 

 a considerable magnetic effect; and the susceptibility of those that 

 occur in the Coal-measures is above the general average. Further, 

 no other rocks that are known to occur, or are likely to occur under 

 the area, have susceptibilities as high as the dolerites found in the 

 Coal-measures. These facts suggest the possibility of the occurrence 

 of dolerites intrusive into Coal-measures beneath the Mesozoic rocks 

 of the Melton Mowbray district. 



Tlie distribution of the dolerites actually proved, and of those the 

 presence of which is suspected by reason of the magnetic dis- 

 turbances, appears to be controlled by the faulting. Moreover, 

 whereas the character of the magnetic disturbances is such that it 

 would not be explained by a sill or laccolite faulted down to the- 

 north, in the manner demanded by the observed throw of the 

 principal fault, it would be explained by an intrusion that had arisen 

 along the fault-plane. The faulting itself is connected with a 

 change of strike in the concealed Coal-measures, and the incoming of 

 doleritic" intrusions in the couceiiled coalfield, in contrast with their 

 absence from the exposed coalfield, appears to depend upon the 

 clianged tectonic features. The change of strike is apparent, but to 

 a less degree, in the Mesozoic rocks which, in the neighbourhood of 

 Melton Mowbray, have suffered a local twist due to the development 

 of an east-and-west anticlinal structure. 



In view of the evidence that later movements have, in this district, 

 followed the lines of earlier and more powerful movements, it 

 appears possible and even probable that this post-Jurassic (probably 

 post-Cretaceous) anticline is situated along the line of a more pro- 

 nounced post-Carboniferous but pre-Permian anticline. In this 

 connexion the isolated position of Charnwood Forest has a consider- 

 able significance. The Forest is situated on the prolongation of the- 

 east-and-west line of uplift, and just at the point where this uplift 

 crosses the line of the more powerful north-westerly and south- 

 easterly (Charnian) uplift. Where the two lines of uplift cross the 

 elevation attains its maximum, and the oldest rocks appear. 



The main line of faulting and of magnetic disturbance is parallel 

 with and on the northern side of the east-and-west anticline, and 

 the faulting is of such a nature that it serves to relieve the folding 

 wliile accentuating the anticlinal structure. It is possible that this 

 belt of magnetic and geological disturbance marks the southern limit 

 of the concealed coalfield. The results obtained by joint magnetic 

 and geological work have thus served to emphasize the real 



