66 UPPER CAMBRIAN. 



W. J. Harrison and he have recognized similar quartzites between 

 Nuneaton and Atherstone, which are overlaid by shales. These 

 are regarded as Cambrian, and grouped as follows : — 



2. Red, grey, and black shales, with hornblendic trap, nearly 2000 feet. 

 I. Thick- bedded quartzite, about 1000 feet. 



This quartzite, known as the Hartshill stone, was formerly regarded 

 by the Geological Survey as Millstone Grit. In the shales (Stock- 

 ingford Shales) previously grouped as Lower Carboniferous, Prof. 

 Lapworth has found Linguhlla ferniginea, Agnostus pisiformis, 

 Kiilorgina cingidata, etc. The beds, which attain a thickness of 

 nearly 2000 feet, are well exposed in the railway-cutting between 

 Stockingford and Nuneaton. At Dosthill, south of Tamworth, 

 shales are also exposed, and these are remarkable for the abundance 

 of worm-tracks. They are named the Dosthill Shales by Mr, 

 Harrison. 



CORNWALL. 



Hard siliceous slaty rocks, schists, and killas, possibly of 

 Lower Cambrian age, have been described by Mr. J. H. Collins 

 under the name of the Ponsanooth Beds, from their occurrence 

 at Ponsanooth, north-west of Penryn, and between Falmouth 

 and Truro. Their character appears to be variable. On the coast, 

 south-west of Pentewan, they consist of hard siliceous rocks ; 

 and they include a number of altered beds, hitherto termed 

 " greenstones," such as the beds largely worked for road-stone near 

 Tresavean Mine, in Gwennap. The black rocks of the Lelant 

 cliffs, and the greater part of the north coast between St. Agnes 

 and St. Ives, are composed of these old rocks. Their thickness is 

 estimated at 12,000 feet.^ 



UPPER CAMBRIAN. 



ORDOVICIAN. 

 LOWER SILURIAN. 



We now come to the Upper Cambrian rocks of Sedgwick, 

 the Lower Silurian of Murchison, the Siluro-Cambrian or 

 Cambro-Silurian of some authors ; a group representing the 

 Second Fauna of Barrande, and including the rocks from the 

 base of the Arenig series to the base of the Llandovery Beds. 



For this series Prof C. Lapworth in 1 879 proposed the; 

 term Ordovician, from the name of the British tribe Ordovices?- 

 This term is sometimes corrupted into Ordovian. 



1 Joum. Roy. Inst. Cornwall, vii. (1881). 



- G. Mag. 1879, p. 13. The term is adopted by Dr. C. Callaway. Ibid. 18S0, 

 p. 118. 



