546 Aubrey Strahan — Rocks beneath the Coal-measures 



evidence we get of the boundary between the Coal-measures and the 

 Silurian shales occurs in the railway south-west of Griff Hollow. 

 The bottom of the railway cutting is in white fireclay with nodules 

 of clay-ironstone, while the wood on the east side is planted over 

 old excavations in flaggy Silurian shales, lying on the top of the 

 thick mass of diorite which is seen at the point where the road 

 crosses the Griff Canal. ' The boundary of the Coal-measures is 

 marked by a shallow " strike-valley," due to the comparative soft- 

 ness of the beds. 



In the Chilvers Coton Eailway-cutting we get a clear view of the 

 Silurian shales, several intrusions of diorite, etc., and of the base of 

 the Coal-measures. In walking from the station southwards we 

 find first grey shales with a thin bed of diorite near the bridge. A 

 few yards south of the bridge these shales pass under a thick mass 

 of diorite, which extends to a distance of 150 yards south of the 

 bridge; there its base is fully exposed. It rests upon shale dipping 

 normally about west-south-west, but thrown into contortions imme- 

 diately under the diorite. The base of the diorite is very straight 

 and forms an angle of 25° with the horizontal. At first sight it 

 resembles a fault of very low hade, but it seems on the whole moi'e 

 probable that its appearance is due to the diorite having broken 

 through and across the shales at the time of its intrusion. Faults 

 are rare in this neighbourhood, but evidences of the intrusive charac- 

 ter of the diorite are abundant. The contortions of the shale more- 

 over do not point to motion in any definite direction along the line 

 of junction, but rather resemble the foldings produced in the leaves 

 of a book by pressure straight upon their edges. 



The shales which lie on the south side of this diorite have a steady 

 dip to W. 10° S. of about 20°— 30°. At 90 yards distance from their 

 junction with the diorite just described, they are found to be split 

 up by numerous strings and sheets of diorite and andesite, ranging 

 from three inches to as many yards in thickness. These intrusive rocks, 

 as is often the case, follow the bedding-planes very closely, so as to 

 imitate contemporaneous lava-flows. But the alteration of the 

 shale above, as well as below, the igneous rock is sufficiently marked 

 to have determined the intrusive character of the diorite, without 

 the conclusive evidence obtainable in other sections. The same 

 shales occupy the cutting for a few yards further, until we are sud- 

 denly made aware of the fact that we have passed the boundary 

 of the Coal-measures by the exposure of a seam of coal on the west 

 side of the railway, as subsequently described. 



The Coal-measures occupy the cutting to a distance of 130 yards 

 south of the Accommodation Bridge, where the Silurian shales are 

 brought to the surface again by a small fault. These shales dip to the 

 north-east, and are highly altered by the influence of a sheet of 

 diorite, which is seen in the cutting to rise from beneath them at 

 45 yards distance from the fault. The same sheet is well seen in a 

 quarry behind Griff Hollow Farm, and in the high road close by. 

 The diorites in this neighbourhood are much decomposed, and show 

 spheroidal weathering even in the thinnest bands. 



