DEVONIAN. 141 



series, and no doubt it is difficult to distinguish with certainty the 

 red sandstones that belong to the Old Red and New Red series. 

 Specimens at Jermyn Street, from the Kentish Town Well, closely 

 resemble rocks of the New Red Series. At the same time the 

 argument that because Devonian rocks are present at Cheshunt 

 and at Meux's Brewery, therefore rocks of Old Red Sandstone type 

 are not likely to occur at Kentish Town, is open to question, 

 because we know that near Torquay rocks of the two types occur 

 near together ; and if the Middle Devonian division is inter- 

 mediate between the Upper and Lower Old Red Sandstone, the 

 argument loses weight.^ 



Econo7nic products, etc., of the Devonian Rocks? 



The Killas, shillet, or clay-slate of Cornwall and Devon varies very much both 

 in colour and in character in different places. It is the matrix of much of the 

 mineral wealth of the district, including ores of tin, copper, silver, lead, and iron. 

 (See sequel.) 



Of Cornish slates, the grey slates of De la Bole west of Camelford, and Tintagel, 

 are most highly valued. The De la Bole Quarries produce roofing-slates, 

 flagstones used for paving-purposes, tombstones, etc. 



Slate has been quarried near Launceston, Tavistock, Plymouth (Cann slate- 

 quarry to north-east), Newton Ferrers, Kingsbridge, Ivybridge, Buckfastleigh 

 (Penrecca slate-quarry), Ashburton, Brixham, and other places in South Devon, 

 and near Wiveliscombe in Somerset. Devonian slate called Kingstone Stone has 

 been quarried near Taunton, on the Quantock Hills. At Hestercombe the slate 

 by contact with a syenitic dyke has become metamorphosed and forms in places 

 a hone-stone. Hone-slate has also been procured from the neighbourhood of 

 Truro. At Tavistock, in Devonshire, oilstones have been obtained. 



The Limestones of Plymouth, Torquay, etc, are largely quarried for building- 

 stone and road-metal, and to be burnt for lime. 



Emery, which is a greyish-black and amorphous variety of Corundum (Alumina), 

 occurs at Madron in Cornwall. The Emery generally used in this country, how- 

 ever, comes from abroad. A remarkable vein of chalcedony, nearly three feet 

 wide, occurs in the cliffs of Perranzabuloe. Axinite is abundant at Lostwithiel 

 and other places. 



Rock Crystal (Cornish diamond) occurs in many parts of Cornwall, at Tintagel, 

 De la Bole Slate Quarries, Carnbrea, etc. Small crystals of quartz have been 

 noticed by Mr. Champernowne in a Devonian dolomite at Ash (or Aish), east 

 of Totnes. 



Beekite (named after the late Dr. Beeke, of Bristol) is abundant in the New 

 Red beds of Torbay, especially at Livermead Head and Paignton. It is found 

 also at Teignmouth and North Tawton. It consists of masses of orbicular silex or 

 annulated chalcedony, and these may originally have been Devonian corals or 

 other fossils more or less completely replaced by silica, for they are sometimes 

 hollow, and in other instances contain a nucleus of fossil coral, shell, or limestone.^ 

 Heavy Spar (Sulphate of Barytes) or " cawk " is obtained from some of the 

 Cornish mines, and manufactured into the paint known as "permanent white." 



^ Whitaker, Guide to the Geology of London, edit. 4, p. 23 ; H. B. W., Geol. 

 Mag. 1886, p. 43. 



■ See also R. Hunt, Bath and W. of Eng. Agric. Journ. xvi ; and J. H. 

 Collins, Mineralogy of Cornwall and Devon, 1871. 



^ S. P. Woodward, G. Mag. 1864, p. 42 ; Pengelly, Trans. Plymouth Inst. 

 1863, p. 18; A. H. Church, Journ. Chem. Soc, and Phil. Mag. Feb. 1862 ; T. 

 R. Jones, P. Geol. Assoc, iv. 454. 



