120 DR. A. H.-COX: REPORT ON MAGNETIC DISTURBANCES IN NORTHAMPTONSHIRE 
susceptibility of these intrusions in the Coal Measures on the flank of the anticline 
gradually predominate over the effects of the older rocks which underly the anticline. 
Hence the “magnetic ridgedine” leaves the anticlinal axis and runs towards these 
highly susceptible rocks. 
We have therefore obtained not only strong evidence that the local magnetic 
disturbances are due to local dolerite Intrusions, but we have also seen that there are 
certain local features in the tectonics of the district, due ultimately to an approach to 
the southern limit of a syncline or basin, which might well account for the local 
occurrence of such intrusions. 
The study of these local tectonic features, the real importance of which is empha¬ 
sised by the. magnetic disturbance, has led to certain conclusions relative to the deep- 
seated structures over a wide area. 
6. The Presence of an Anticlinal Structure in the Mesozoic Rocks. 
The south-easterly twisting of the Coal Measure strata was imparted, as already 
stated, as the result of a movement of pre-Permian age, and it applies to the strata 
of the concealed coalfield. The structure is not visible on the geological map, as the 
concealed coalfield is overlain by strata of the Permian, Triassic, and Jurassic 
Formations. These Formations sweep across country in a general north—south to 
north-north-east—south-south-west direction, in accordance with the usual trend of 
the Mesozoic strata, and apparently regardless of the structures among the older 
Formations below. 
It will be recalled that the Cinderhill Faults (p. 117) showed that movements had 
been renewed in post-Triassic times along the lines of the earlier pre-Permian move¬ 
ment and that, as a result, the faults had a greater throw in the Coal Measure strata 
below than in the Permian and Triassic beds above. With this clear example before 
us, we may proceed to search for further indications of the Mesozoic rocks being 
affected by movements along lines initiated in Palaeozoic times. Such indications are 
not far to seek. 
The regularity of the north-north-east—south-south-west sweep of the Mesozoic 
rocks suffers a remarkable interruption within the district under consideration. 
This is best seen in the outcrops of the Rhsetic and Lower Lias Formations. These 
follow a regular north—south course for 50 miles from the Humber in the north to a 
point south of Newark. Then they turn south-west for 15 miles as far as the Leak 
Hills, in the angle between the Trent and Soar Valleys. At the Leak Hills the out¬ 
crop swings round in a right-angled turn and strikes south-east for 10 miles as far as 
the Sileby Fault (p. Ill), in the Wreak Valley. Immediately after crossing the fault 
the strike turns south-south-west and continues in this direction for about 50 miles 
ro the southern parts of Warwicksliire. 
