926 



IRON 



* There can be no doubt that the lithomarge and bole alternating with compact 

 basalts are but decomposed basalts. The passage from basalt to lithomarge and bole 

 can be traced in all cases ; not unfrequently large masses of basalt are to be seen in 

 the midst of the lithomarge, the concentric layers presenting all the varieties of 

 texture and colour between the hard and black basalt of the interior and the purple 

 or yellowish argillaceous masses in which the basalt appears to be imbedded. Again, 

 the boles often contain cavities filled with the ordinary zeolites of the amygdaloid 

 basalts. 



' Observations in the field and the preceding comparative analyses go far to prove 

 that the bole and lithomarge are the resultants of aqueous action in combination with 

 acidulated gases, which, dissolving out certain mineral substances, has effected the 

 decomposition of the basalts, especially of the more felspathic ones.' Tate and 

 Holdcn. 



The following is a series of analyses of Forest of Dean ores, by Dr. Noad : 



This brown iron ore is also found at Alston Moor and Weardale, Durham, but is only 

 used to a limited extent on account of its association with lead and zinc. It occurs at 

 Llantrissant, near Cardiff; in many parts of Devon, especially at Smallacombe, near 

 Newton Abbot ; and at Sharkam Point, near Brixham. It has also been recently found 

 at Poltimore, near South Molton, in Devonshire, much of it containing considerable 

 quantities of manganese. In Cornwall the brown haematite is worked at Restormel, 

 near Lostwithiel ; at several places around St. Austell; in Constantino; and other parts. 



Some of the brown haematites contain a large percentage of manganese. Their 

 general composition is illustrated in the following analyses (Dr. Noad) : 



The brown iron ores of the secondary formations have of late years assumed 

 considerable importance. In the Lias, the Oolite, and in the Lower Greensand for- 

 mations, brown haematites (that is, hydrated oxides of iron), generally impure and 

 sandy, are found. They range almost continuously from the northern parts of Wilt- 

 shire to the wolds of Yorkshire, passing through Oxfordshire, Northamptonshire, and 

 Lincolnshire, appearing as an ochreous brown oolitic rock. The most important bed 

 is that occurring in the lower part of the great oolite, from the neighbourhood of 

 Banbury through Northamptonshire. The extent of the workings in Northampton- 

 shire will be best judged of by the following details of the quantities of iron ore 

 produced from the mines of Northamptonshire in 1872 : 



