S36 Geological Society ;— ^ 



north and south joints, or, in other words, intersecting the strata at 

 right angles. 



In some instances, however, they have an east and west course, 

 and are found associated, in this condition, with the siliceous lime- 

 stones which possess only the principal system of joints. 



These dolomites, from their mode of occurrence, have had their 

 origin subsequent to the production of the joints, and are often 

 found thinner below than above. From the circumstances of their 

 occurrence, the author is disposed to regard them as metamorphosed 

 ordinary limestones ; and the metamorphic action he is disposed to 

 attribute to sea- water, which, containing sulphate of magnesia, has 

 found access, by means of the joints, into the limestone masses ; and 

 this, at an elevated temperature, combined with pressure, has pro- 

 duced these changes, by the double decomposition of sulphate of 

 magnesia and carbonate of lime, and, by this means, given rise to 

 the production of the dolomites occurring in this neighbourhood. 



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

 Rag." By W. Hawkes, Esq. 



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

 furnace, and after a slow cooling during thirteen days, it presented 

 an 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 under the vesicular layer was solid stone, 

 interspersed here and there with air-bubbles). Mr. Hawkes added 

 some observations relating to the results of experiments which he 

 had made to ascertain the temperature of melted cast iron, and of 

 melted basalt. 



3. " On the Iron Ores of Exmoor." By Warington Smyth, Esq., 

 M.A., Sec. Geol. Soc. 



The author described the occurrence of ores of iron within a 

 district, of about thirty miles in length, between Ilfracombe and the 

 Bridgewater Flats, in slaty rocks belonging to the " grey wacke " of 

 De la Beche's " Report on Cornwall," or to the " Plymouth group" 

 of the Devonian System, as described by Sedgvvick 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 Combe 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 which have recently been explored in the Brendon Hills, 

 and tested on the property of F. W. Knight, Esq., M.P., are so 

 nearly conformable to the beds of slate, striking about E. 10° S., 

 with a dip of from 45° to 65° southward, that they might be easily 

 taken for stratified deposits. 



