Xlii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



But nowhere is the quantity so great, the variety so remarkable, 

 the richness carried to such a height, as in the eastern moorlands of 

 Yorkshire, where in and above the lias are at least thirteen noticeable 

 bands of iron-ore, more than one of them yielding above 40 per cent. 

 of iron (in selected examples 50), two of them so thick and so purely 

 ferruginous as to yield, one from 20,000 to 50,000 tons per acre, the 

 other from 10,000 to 100,000 tons. This last, in its best state, near 

 Eosedale Abbey, is magnetic with polarity, and purely oolitic, with 

 scarcely any earthy impurity, and hardly a shell, or coral or crinoid, 

 or fossil of any sort in its dark blue mass, 32 feet in thickness. It 

 lies at the very base of the Oolitic formation, — upon the top of the 

 Lias. 



On reviewing the circumstances under which these great stratified 

 deposits of iron- ore are found, we observe that, in general, they ap- 

 pear in the parts of the strata which geographically approached the 

 ancient shores, — they are even most abundant in the freshwater 

 portions of the deposits — as, e.g. in the Weald of Sussex, at Seend 

 in Wiltshire, in Shotover-hill, in the Moorlands of Yorkshire. The 

 mechanical origin of the deposits by drifting is thus put in evidence. 

 The occurrence of plants, and even coal-beds, iu these same tracts, 

 is easily seen to be probable, and it is the fact, though the carbo- 

 naceous deposits are of small value. 



In the view of Prof, W. B. Eogers this association of the carbo- 

 naceous element with argillaceous iron-ore is necessary — ^the iron 

 appearing as it does in consequence of the action, on minerals which 

 contain it, of the carbonic acid which is generated by the decay of 

 the vegetable masses. The magnetic ironstone of Eosedale seems 

 to suggest a view of the same kind, without the necessity of supposing 

 the actual state of the oxide of iron to have been accomplished by 

 changes on the spot. 



Let us imagine a silicate of peroxide of iron (as augite), in a state 

 of decomposition, to which the reducing agency of free carbonic acid 

 and water should be applied while nascent from decomposing animal 

 or vegetable matter. The result might be a mixture of peroxide and 

 protocarbonate of iron with silica, carbonate of lime, and some other 

 less essential matters. It is probably to this composition, partly 

 peroxide and partly protoxidated iron, that the magnetic quality of 

 the ore is due. I am happy to say that Mr. Sorby is still engaged in 

 those ingenious researches into pseudomorphism which have already 

 enabled him to exhibit the substitution of carbonate of iron for car- 

 bonate of lime, without change of form or crystalline structure. 



Not to speak at present of the rich ores of iron which occur in the 

 west of Somerset* and north of Devon f, or of the magnetic ore which 

 occurs in the veins of Snowdonia, I may add a few words on the very 

 rich and abundant deposits of red peroxide which lie in the limestone 

 tracts of West Cumberland andlSTorth Lancashire. Partially stratified, 

 covered by limited stratification, and resting on limestone, these 



* From information communicated by Sir Walter Trevelyan. 

 t Professor W. W. Smyth on the Iron-ores of Exmoor, Quart. Journ. Geol. 

 Soc. vol. XV. p. 105. 



