662 Transactions. — Chemistry and Physics. 



the coal, Hull* says, " Nor was this alteration 

 accompanied by outburst of igneous rocks, or by violent 

 crumplings and contortions of the beds . . ; on the con- 

 trary, the strata are usually but slightly thrown out of the 

 horizontal position. Other causes must therefore be sought 

 for. . . . We may offer conjectural solutions of it, such as 

 the greater increase of temperature over the western or an- 

 thracitic region as compared with that over the eastern ; or 

 that owing to fissures exceptionally numerous in the western 

 area greater facility was afforded for the escape of the gaseous 

 products. But none of these reasons are quite satisfactory, 

 and this remains one of the problems in physical geology 

 which yet awaits solution." 



Both the causes directly mentioned above — rise of tem- 

 perature and increase of pressure — seem competent to bring 

 about the chemical action necessary for that gradual elimina- 

 tion of oxygen and hydrogen which produces an anthracite 

 from an ordmary hard or even a soft hydrous variety of coal. 

 In the case under consideration — the Brockley — there is 

 abundant evidence also of both. The dyke is large, and, even 

 if, as seems at first sight most probable, it is the result of a 

 single effort of injection,! must have elevated the temperature 

 of the surrounding strata considerably during a long interval 

 of time. 



That enormous local pressure must also have been brought 

 into play is evident from the fact that the measures have been 

 thrown into a vertical position by the dyke, and in part actu- 

 ally overturned. 



The two causes are also almost inseparably connected. 

 Increase of pressure would certainly result in increase of 

 temperature| and chemical action dependent thereon, even 

 if the rise of temperature were not evident, and the increase 

 of temperature due to the injection of the dyke would in many 

 instances be followed by a great increase of pressure as the 

 mineral masses composing it took solid form.§ 



The Brockley dolerite dyke has certainly come close enough 



* E. Hull, " The Coalfields of Great Britain," 3rd ed., p. 259. 



t Such a dyke is usually fairly homogeneous, and therefore probably 

 fills a fissure opened by the pressure accompanying its injection. (See 

 O. Fisher, " Physios of the Earth's Crust," p. 283.) 



I Mr. Sorby has suggested that under the conditions which exist 

 •within the earth's crust there may be even a direct conversion of 

 mechanical into chemical energy, and that many familiar geological 

 phenomena will have to be explained in this way. (Proc. Roy. Soc, 12, 

 p. 538.) 



§ The result of recent experiments appears to show that such sub- 

 stances as whinstone and granite are less dense in the solid than in the 

 liquid state at the melting temperature, and must therefore expand on 

 solidifying." (Fisher, op. cit., p. 291.) 



