CAB 



[72] 



CAR 



world have been preserved and 

 converted into beds of mineral coal. 

 The most characteristic type that 

 exists in this country of the 

 general condition and circumstan- 

 ces of the strata composing the 

 great carboniferous order, is found 

 in the north of England. Accord- 

 ing to Mr. Forster's section of the 

 strata from Newcastle-upon-Tyne 

 to Cross Fall, in Cumberland, it 

 appears that their united thickness 

 along this line exceeds 4,000 feet. 

 This enormous mass is composed of 

 alternating beds of shale, sandstone, 

 limestone, and coal. 



The above group constitutes in 

 the Rev. J". Conybeare's arrange- 

 ment the Medial order ; he says 

 " this series of rocks is by some 

 geologists referred to the flcetz, by 

 others to the transition class of the 

 "Wernerians; we have preferred 

 instituting a particular order for 

 its reception, a proceeding justified 

 by its proportional importance in 

 the geological scale, its peculiar 

 characters, and the many inconve- 

 niences arising from following 

 either of the above conflicting 

 examples." 



Sir R. Murchison in his splendid 

 work " The Silurian System," says 

 " Being convinced that the Old 

 Red Sandstone is of greater magni- 

 tude than any of the overlying 

 groups, I venture for the first time 

 in the annals of British geology to 

 apply to it the term system, in 

 order to convey a just conception 

 of its importance in the natural 

 succession of rocks, and also to 

 show, that as the carboniferous 

 system, in which previous writers 

 have merged it, (but from which it 

 is completely distinguishable, both 

 by zoological contexts and litholo- 

 gical characters) is surmounted by 

 one- red group, so it is underlaid by 

 another, this lower red group 

 being infinitely thicker than the 

 upper." 



Mr. Mushet, from a careful ex- 

 amination of the Forest of Dean, 

 has given a list of the various beds 

 of the coal measures, carboniferous 

 limestone, and old red sandstone, 

 constituting a mass of 8,700 feet 

 in thickness : the coal measures 

 being 3060 feet in depth. The whole 

 reposes on the grauwacke limestone 

 of Long Hope and Huntley. 



CAEBONIFEKOTJS LIMESTONE. The name 

 proposed by Mr. Conybeare to be 

 given to mountain limestone. See 

 Mountain Limestone. 



CABBO'NIC ACID. A compound of 

 carbon and oxygen ; it has been 

 called aerial acid, fixed air, creta- 

 ceous acid, and mephitic gas. 

 Carbonic acid is very plentifully 

 disengaged from springs in almost 

 all countries, but especially near 

 active or extinct volcanoes. This 

 elastic fluid has the property of 

 decomposing many of the hardest 

 rocks with which it comes in con- 

 tact, particularly that numerous 

 class in whose composition felspar 

 is an ingredient. In volcanic 

 countries these gaseous emanations 

 are not confined to springs, but 

 rise up in the state of pure gas 

 from the soil in various places. 

 The Grotto del Cane, near Naples, 

 affords an excellent example. The 

 acid is invisible, is specifically 

 heavier than atmospheric air, and 

 on this account accumulates in 

 any cavities on the surface of the 

 ground. It may be dipped out of 

 any excavations in which it has 

 accumulated, poured into a bottle, 

 like water, corked, and carried to 

 any distance. It is fatal to human 

 life when breathed undiluted, and 

 by the miners it is called choke- 

 damp. Carbonic acid gas is evolved 

 abundantly in coal pits. M. 

 Bischof calculates that the exhala- 

 tion of carbonic acid gas, in the 

 vicinity of the lake of Laach, 

 amount to 600,000 pounds daily, 

 or 219,000,000 pounds in a year. 



