100 DE. A. H. COX; REPORT ON MAGNETIC DISTURBANCES IN NORTHAMPTONSHIRE 
Whitwick, and it was pierced in a bore-hole at Northampton,* 35 miles south of 
Melton Mowbray. 
The next Formation that might be present is the Silurian. Some calcareous 
mudstones and limestones touched in a boring at Hathern, in the Soar Valley, have 
been thought to be possibly of Silurian age. t 
The possibility that Cambrian rocks are present must be considered, though they 
nowhere outcrop at the surface of the district in question, nor have they been proved 
by bore-holes, which, as a rule, naturally cease before Cambrian rocks could be 
entered. But it must not be forgotten that at Nuneaton, Cambrian rocks, with 
associated intrusive igneous rocks (camptonites), directly underlie the Coal Measures. 
Further Cambrian rocks have been proved in a boring at Leicester,! 15 miles south¬ 
west of Melton Mowbray, where they were found underlying Trias at 837 feet below 
tbe surface. To the west of Leicester, Cambrian rocks, with associated igneous 
intrusions, have been pierced at various points near Market Bosworth.§ More recently 
Cambrian shales, again with intrusive rocks, have been found directly to underlie the 
Lower Lias at Calvert, Buckinghamshire, at a depth of only 480 feet.|| Thus the 
Cambrian strata with their associated intrusions evidently have a considerable under 
ground range in the eastern Midlands. 
The oldest rocks seen are the Pre-Cambrian rocks (Charnian), which crop out 
at the surface in Charnwood Forest, where they appear directly from beneath the 
Keuper Marl or Sandstone. They consist of a thick series of ashes, agglomerates, 
and slates, with abundant associated igneous rocks of various kinds, the majority 
intrusive, but some perhaps extrusive. The Charnian ridge strikes north-west— 
south-east, and although sinking under the 4’rias, it evidently continues in a south¬ 
eastern direction for a considerable distance under comparatively shallow cover. 
This is proved by the fact that the Charnian rocks were pierced in a boring at Orton, 
Northants (see p. 93), while igneous rocks of a type common in Charnwood Forest 
actually appear at the surface at Croft, and at various other points in South 
Leicestershire. 
To the north-east, however, the plane of junction between the Charnian rocks and 
the overlying Trias is very irregular, and it often dives rapidly underground, so that 
the Charnian rocks soon become buried beneath a considerable cover. Therefore 
H. J. Eunson, “ Palaeozoic Rocks beneath Northampton,” ‘Q. J. G. S.,’ vol. XI. (1884), pp. 484 
and 495. 
t The cores from this boring, put down in 1876, were unfortunately never inspected by any geologist 
who was able to leave a satisfactory record, so that the results are entirely lost. (See “ The Geology 
of Burton . . . and Loughborough,” ‘Mem. Geol. Survey,’ 1905, p. 54.) 
t “The Geology of Leicester,” ‘Mem. Geol. Survey,’ 1903, p. 63. 
§ “The Geology of Leicestershire and South Derbyshire Coalfield,” ‘Mem. Geol. Survey,’ 1907, 
p. 344. 
II A. Morley Davies and J. Pringle, “ Deep Borings at Calvert Station . . . ‘ Q. J. G. S.,’ 
vol. LXIX. (1913), p. 308. 
