CXn* PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



with certain other minerals, such as some belonging to the fels])ar 

 family and sulphuret of iron. 



In the progress of the Geological Survey during the past year in 

 Ireland, we had an opportunity of seeing a beautiful arrangement of 

 dolomite crystals in ordmary limestone on the south of Carlow, near 

 Bagenalstown. In that part of Ireland there is a dolomitic series of 

 beds amid the accumulations of the carboniferous or mountain lime- 

 stone, having a considerable range. In the higher parts where this 

 series is surmounted hy certain dark and black shales, the beds, which 

 may, for convenience, be termed those of passage, show the cessation 

 of the conditions under which the crystals of dolomite were so de- 

 posited as to form the whole or nearly the whole of the strata. 

 There were alternations of circumstances, and little sheets of crystals 

 of the carbonates of lime and magnesia, often of slight depth, alternate 

 with the common dark carbonaceous limestone, the light colour of 

 the one, in sections, strongly contrasting with the dark colour of the 

 other. We here seem to have had tim.es when these crystals of the 

 carbonates of lime and magnesia were strewed over the bottom, at 

 first so little mingled with other matter as to constitute whole beds, 

 and then so mixed, as conditions changed, that they were only 

 strewed about in patches, their production finally ceasing altogether. 



Many other facts, as you are aware, upon the great scale, could be 

 adduced to support the view that, at least, some of the dolomitic rocks 

 have been the result of deposit from water, as indeed we might ex- 

 pect, and we would here recall to your attention that numerous lime- 

 stones contain carbonate of magnesia, besides the rocks properly 

 termed dolomites, and often far more abundantly than would be 

 supposed. We should also not feel surprised that when a deposit 

 was eifecting from solution in water, and the carbonates of lime and 

 magnesia were being thrown down in certain definite proportions (and 

 the pro])ortions those of bitter spar or dolomite), that crystals were 

 the result (supposing the needful time for the definite arrangement of 

 the component particles), their arrangement in beds or thin laminae, 

 intermingled with ordinary limestone, being dependent on circum- 

 stances. 



Satisfied as we may happen to be, however, with such a view as afford- 

 ing an explanation of the mode of occurrence of dolomitic rocks in 

 certain districts, it by no means follows that it will sufiice for all do- 

 lomites wherever found. Other views have been taken and ably sup- 

 ported. You are familiar with the opinions and facts adduced by 

 Von Buch, respecting the occurrence of dolomite in certain districts, 

 as also with the writings of others entertaining the same views. 

 During the past year some highly interesting experiments have been 

 made by M. de Morlot, the results of which are considered by him 

 to support the metamorphic character of dolomites, more particularly 

 in the manner advocated by M. Haidinger. 



A notice of these experiments and conclusions is contained in a 

 letter of M. de Morlot to M. Elie de Beaumont, in which he refers 

 to the calculations of this distinguished geologist '■' respecting the 

 * Bulletin de la Societe Gcologique de France, 1837, pp. 174-177. 



