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masses, either in the form of nodular or lenticular concretions, 

 or bands, in both of which conditions it is intimately associated 

 with the Coal seams of the Lower Coal Measures, especially 

 those worked in the Kingswood district, at Ashton, near Bristol, 

 and the Pitcot area immediately north of the Mendip Hills. 

 This massive Siderite, or Clay Iron-stone, occurs also in the 

 Argillaceous group of rocks termed Lias, Oxford, Kimmeridge, 

 and London Clays; and hence the common practice of recogniz- 

 ing and naming these ores according to the formations in which 

 they occur. No enquiry is so wide and interesting as the 

 relation which mineral veins hold to the rocks which enclose 

 them, or with which they are intimately associated. With veins 

 filled with other ores than those of Iron, the origin of the metallic 

 accumulations may generally be referred to causes acting from 

 within, (esoteric,) or distant centres in the interior, assisted by 

 those subterranean changes which are the universal result of 

 those calorific and sublimitic agents that are always at 

 work in the earth's crust. The origin of these various ores, in 

 their different matrices, and under so many conditions, is yet a 

 problem for solution, and is a difficult one to determine; but I 

 have in this communication endeavoured to account for the mode 

 of occurrence, position, and condition of the Hydrous Oxides of 

 Iron so abundantly distributed in the faults and veins of the North 

 Bristol Coal Basin. I now come to the Geological position, 

 place, or age of these Minerals in question; and from careful 

 observation and examination, both in this area and others 

 in the district, have no hesitation in referring the origin of 

 these extensive lode accumulations or deposits of Hydrated 

 Peroxides, or Brown Haematite Iron Ores, to the age of the New 

 Eed Sandstone: that is to say, the fissures, faults, &c., which 

 occurred in the older rocks (prior to the deposition of the New 

 Red) were filled up, in a manner I hope to make clear, during 

 the period of the accumulation of the Trias group of rocks, 

 either through chemical changes, or mechanical suspension or 

 infiltration. It is well known and understood that the whole of 

 the Palaeozoic rocks of this area, like all others, were placed in 

 their present disturbed position, after having gone through the 

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