170 New Publications. 



being generally of a conieal form, of no exceedingly ancient 

 origin, burning with no extraordinary intenfity of internal 

 heat, and not half fo numerous as Come wildly theoretic 

 niineralogifts have fuppofed them to be. 



In that which we fliould incline to confider as the eighth 

 Effay, Mr. Kirwan endeavours to explain the internal ar- 

 rangement of mountains. He here relates that their mate- 

 rials are difpofed cither in irregular heaps or in beds or ftrata, 

 horizontal, varying from that pofition by au angle, of from 

 5^ to 40% or fometimes even almoft vertical. Sometimes 

 the ftrata run in the direftion of the declivity of the moun- 

 tains they compofe, and fometimes their courfe is direftly 

 oppofuc to this. Mountains of primitive limeftone arc often 

 in irregular piles, but often, too, horizontally ftratifjed. Of 

 fecondary calcareous ftrata, the ftrufture is commonly hori- 

 zontal. The ftrata of fecondary mountains, for the moft 

 part, afcend towards the primary.— ^Thefe are fbme of the 

 leading truths unfolded in this Eftay. 



Coal-mines are the fubjects of the ninth Eflay. Pit-coal 

 is a compound of bitumen with carbon: its fpecific gravity 

 is from 1,23 to 1,500. The foils within which beds of coal 

 ufually occur, are argillaceous, arenilitic, trappofe, or calca- 

 reous. Thefe arc difpofed in ftrata over the coal, or in alter- 

 nation with its ftrata. The thicknefs of the ftrata, or Teams 

 of coal, varies from half an inch even to ^o feet. Shale, bi- 

 tumiTious fliale, or fandftone, arc the ftones which generally 

 form both the roof and Jioor to /earns of pit-coal. Some- 

 times thefe fcams are in their difpofition horizontal. They 

 rife at times to angles of from 2^° 1045° with the horizon, 

 It cannot be true that, as has been fuppofed by Genfanne, 

 pit-coal is nothing but argillaceous matter impregnated with 

 petrol or afphall; nor that this coal is entirely of vegetable 

 origin 5 nor that it is formed from the fat and unttuofity of 

 the ariimals of the ocean. The ftrata of this mineral fcem 

 rather to have been formed in confequence of the difintcgr^-r 

 tion of many of the primitive mountains by the homoge- 

 neous union of the petrol ^.nd carbon which were bv that 

 difintegration liborate4 out of the compofition into which 

 tJiey h^^ originally entered. Coal is therefore to be fought, 



with. 



