ORIGIJSr AND DEVELOPMENT OP ORE-DEPOSITS. 179 



At Lyme Regis the lias-clay, as is well known, contains 

 numerous calcareous concretions.'^' Concretionary beds of 

 earthy carbonate of iron (clay iron ore) have been met with 

 associated with the anthracite beds of North Devon, at Bideford, 

 and Chittlehampton, although not, I believe, to a sufficient 

 extent to be of economic importance ;f such beds in the 

 carboniferous rocks of Staffordshire and Wales are, however, of 

 the highest importance. 



The same may be said of the concretionary and nodular 

 iron pyrites which has been met with in the "killas" in many 

 parts of the West of England. These are of economic impor- 

 tance in the chalk of Kent and Sussex, and in the London clay 

 at Sheppey and elsewhere. Concretionary patches of peroxide 

 of iron occur on a small scale in some of the sandstones of the 

 Ladock district, as also in some of the elvans. These also are 

 too small to be of economic value. ;|: 



A singular specimen, " resembling a chalk flint," which was 

 found in tho lode at Balleswidden, was described in 18^5, by 

 Mr. S. Higgs. It occurred in a vugh at the 130 fathom level, 

 and was surrounded by decomposed felspar and quartz granules. 

 Mr. Higgs thought it had fallen in from the surface, but its 

 mode of occurrence and surroundings rather suggest that it was 

 a concretion of siliceous matter. § 



Mr. Hen wood mentions some " globular concretions " in the 

 lodes at Wheal Duffield, Relistian, Trevaskus, and Wheal 

 Herland, containing kernels of slate, granite, elvan, and copper- 

 pyrites, and says similar concretions exist in the country rocks. || 

 Dr. Le Neve Foster, — who saw similar masses in the lode at 



* In these a lamellar structure is often developed, parallel to the bedding and 

 lamination of the containing rock. This is doubtless a subsequent development, 

 arising either from pressure, or perhaps from transverse electric currents as will be 

 shewn hereafter. 



f Delabeche, Report on Cornwall, &c., p. 125. 



I The concretionary aggregations of peroxide of iron in the sands of Sussex 

 were formerly the source of all the iron used in the South of England — and this 

 for a long series of years. 



§ Trans. E.G.S.C., ix, 1865, p. 1. 



Trans. E.G.S.C., v, p. 39, 



