306 



fHE GEOLOGIST. 



2. " On an Experiment in melting and cooling some of the Rowley Eag." By 

 W. Hawkes, Esq. Communicated by the President. 



About 31 cwt. of basalt was melted in a large double reverberatory furnace, and 

 after a slow cooling during 13 days, it presented un upper stratum of stony 

 vesicular matter, about 1 inch thick, next a layer of black glass, from 2 to 8 inches 

 deep on that side of the mass which was exposed to the air from the door of the 

 furnace (elsewhere, immediately imder the vesicular layer was solid stone, inter- 

 spersed here and there with air -bubbles). Mr. Hawkes added some observations 

 relating to the results of experiments which he had made to ascertain the tempera- 

 ture of melted cast iron, and of melted basalt. 



3. " On the Iron ores of Exmore." By Warington Smvth, Esq., M.A., Sec. Geol. 

 goc. 



The author described the occurrence of ores of iron within a district of 

 about thirty miles in length, between Ilfracombe and the Bridgewater Elats, in 

 slaty rocks belonging to the " greywacke " of De la Beche's " Eeport on Cornwall," 

 or to the " Plymouth Group " of the Devonian System, as described by Sedgwick 

 and Murchison. They are situated partly to the north, but chiefly to the south, 

 of the irregular bands of limestone which pass from Combe Martin eastward by 

 Simonsbath to Cutcombe and Treborough.- The really stratified deposits of iron- 

 ore are bands of argillaceous nodules, alternating with shales, similarly to those of 

 the coal-measures; and these have been found in abundance on the flank of 

 Hangman Hill near Comb Martin, and in the north forest of Exmoor ; but in 

 general, their angle of inclination is too great to allow of their being worked in 

 competition with the analogous ores of the coal-fields. 



The lodes containing iron-ore, extensively worked some centuries ago, and v>'hicli 

 have recently been explored in the Brendon Hills, and tested on the property of 

 E. W. Knight, Esq., M.P., are so nearly conformable to the beds of slate, striking 

 about E. 10 degs. S., with a dip of from 45 degs. to 65 degs. southward, that they 

 might be easily taken for stratified deposits. 



In several places, as at Cornham Ford, the Eoman lode, and the little Woolcombe 

 lode, haamatite has been found at or near the surface, containing 98"4 per cent, of 

 peroxide of iron, in masses which present the structure of sparry iron or carbonate. 

 Most of the lodes, however, especially those, of the Deer-park on Exmoor, and 

 Ealeigh's Cross, consist of brown or hydrous peroxide, generally occurring m large 

 cavernous masses, with the interior of the cells often lined with brilliant but 

 minute crystals of Goethite (pure hydrous peroxide), yet exhibiting the rhombo- 

 hedi'al structure of sparry ore. Analysis shows this ore, especially from certain of 

 the Exmoor veins, to contain 71'3 per cent, of peroxide of iron, together with a 

 considerable per-centage of oxide of manganese. 



Lastly, several of the veins prove in depth to consist of sparry ore (siderite or 

 carbonate of iron), containing a notable per-centage of carbonate of manganese. 

 This has especially been shown at Goosemoor, Huel Eliza, Hangley Cleave, and on 

 Iventisbury Down. The width of these veins varies from a few inches to above 20 

 feet, and at the greatest depth hitherto reached, 110 feet, there is no deteriora- 

 tion in size. Quartz -veinstone and fragments of slate occasionally fill part of the 

 lodes, and this fact, coupled with the interruptions of " slides " and " heaves," has 

 led to some misplaced disa]3pointment on the part of those who made their 

 calculations without taking into account the capricious natm'c of true veins. 



Hence it appears, — 1st, that the vein-fissm-es have been formed in this district 

 almost solel}^ in planes conformable to those of stratification, and that, after 

 having been filled with carbonate of ii'on, quartz, &c., they have been more or 

 less disturbed. 



2ndly. Tliat the sparry ore has been converted, often to a great depth, into 

 Goethite or pure hydrous peroxide, the consequent decrease of bulk giving rise to 

 the cellular cavities lined with crystals. 



3rdly. 'J'liat some smaller portions have been converted into lia?matite, having 

 probably passed through the intermediate stage of brown peroxide. 



4thly. The i^ebbles of hannatite at the base of the New Eed in the adjoining 

 district appear to be derived from these lodes, and would indicate their having 



