540 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



many geologists, seems to us in the highest degree improbable, for 

 the reason that true graphite has never been found — so far as our 

 knowledge goes — in connection with coal, whether the latter be in its 

 ordinary bituminous condition or in its nearest approach to pure carbon 

 as anthracite, as it ought to be if it was formed in the same way in 

 which coal has been, and was only the canying forward of that process to 

 the last stage of carbonization. If graphite was the final result of the 

 working of the agencies by which vegetable matter has been turned 

 into anthracite, it seems impossible that, somewhere in the vast area 

 covered by the anthracitic formation in this and other countries, there 

 should not be at least some distinct traces of graphitic material found. 



It is stated in the various text-books of mineralogy and geology, that 

 graphite has been formed by the passage of dikes of eruptive rock 

 through coal beds. This, however, does not seem to be confirmed by 

 the result of more recent and more careful observations than those made 

 in the days to which many of the statements in our text-books belong. 

 So far as our own observations go, the tendency of the eruptive rocks, 

 in their passage through coal, is to change this into a material very dif- 

 ferent in character from graphite. 



Much of what is called " plumbago " is by no means graphite. It is, 

 rather, a mixture of particles of carbonaceous matter with rock ; the 

 result being, in certain cases at least, a refractory material which can 

 be used for some of the purposes for which graphite is employed. We 

 repeat, therefore, that we have never seen, and know of no authentic 

 account of any one else having seen, pure graphite and coal so associ- 

 ated together as to make it necessary to believe that the former was 

 produced by the decomposition of vegetable matter, as we have abun- 

 dant reason to believe that coal in all its forms has been. 



The graphite which is formed artificially at the present day is, so far 

 as we know, exclusively the result of operations carried on at a high 

 temperature.* The separating out of graphite in cast-iron and slags, 



* The same may be said of the more or less successful attempts to make artificial 

 diamonds. The experiments of Mr. Hanuay in this line, in which he claims to 

 have succeeded in forming this gem, although by no means affording any encourage- 

 ment for the belief that it can be manufactured with pecuniary profit, seem to have 

 resulted in the production of something which had the physical characters of the 

 diamond. High temperature and immense pressure were the most important factors ; 

 but it is stated by Mr. Haunay that the presence of nitrogen seemed to be a sine qua 

 non. This last-mentioned item may be noticed in connection with what is said 

 farther on in the text in reference to the part played by cyanogen in the formation of 

 artificial graphite. 



