and around the Warwickshire Coal-field. 543 



pre-Carboniferous age, and do not affect the Coal-rneasnres in any 

 way whatever. 



The total thickness of the Coal-measures, as now shown, amounts 

 to between 600 and 700 feet, in place of about 3000, as previously. 



It will be convenient in describing these rocks to take them in 

 order of age, beginning with the southern end of the range of each 

 formation. 



The Caldecote Series. 



The oldest rocks are found near Caldecote, rising from beneath the 

 quartzite on the north-east side of the range of low hills, which this 

 rock forms between Nuneaton and Hartshill. They are referred to 

 by Professor Lapworth as the Caldecote Volcanic Series, and consist, 

 as he pointed out to me, of a finely-laminated rock, probably a tuff, 

 with intrusions of diabase and quartz-porphyry. 1 There are very 

 few exposures of these beds. About a quarter of a mile east of 

 Caldecote Windmill, there is an abandoned quarry known as the 

 ' Blue Hole,' from which paving cubes were formerly obtained. 

 The rock in request was the diabase, but the workings on the north 

 side intersected quartz-porphyry, which had been intruded into, and 

 contained fragments of, a highly altered fine-grained ash. The 

 diabase with a sharply-defined line of separation is found in the side 

 of the quarry above the quartz-porphyry. Its intrusion is con- 

 sidered by Professor Lapworth to have taken place subsequently to 

 that of the quartz-porphyry. 2 The tuff has been found again by 

 Professor Lapworth in the entrance to an old tunnel 100 yards west 

 of Caldecote Hill, where the presumed bedding-planes have a dip 

 25° to 30° in the same direction as the quartzite, that is, about 

 south-west. The further extension of these beds is inferred from 

 the occurrence of fragments in the soil, and from the position of the 

 overlying conglomerate, which will now be described. 



The Hartshill Quartzite. 



The Hartshill quartzite extends from the Midland Station at Nun- 

 eaton to half a mile north of Hartshill, with a steady dip to the 

 south-west of from 25° to 45°. The whole series can be seen in the 

 series of immense quarries in which it is worked for road-metal. 

 The base of the quartzite is a coarse stratified conglomerate or breccia, 

 containing fragments of the underlying Caldecote series, some of the 

 fragments ranging up to the size of half a brick, as was pointed out 

 to me by Prof. Lapworth. The base is seen in the cutting by which 

 Boon's Quarry is entered, about one-third of a mile south-east of 

 Caldecote Windmill. The quartzite becomes coarse in grain towards 

 the base and passes into a grit made up of small rounded grains of 



1 These rocks were referred to by Sir Andrew Ramsay in his evidence given 

 before the Coal Commissioners as being of doubtful origin (Report of Coal 

 Commission, vol. ii. p. 470j. Eventually from the limited nature of the exposures, 

 and the small advance that petrography had made at the time of the publication of 

 the map, they were included in the index with the intrusive diorites under the 

 general name of greenstone. 



2 Geol. Mag. for 1886, p. 320. 



