218 ANNUAL OF SCIENTIFIC DISCOVERY. 



well known to be nearly pure carbon, for it leaves in burning but a 

 very small quantity of ash. Xow, if these primitive crystalline rocks 

 are of igneous formation, it is impossible to explain how graphite 

 could coexist with silicates of protoxyd of iron without having re- 

 duced these salts ; judging merely by what takes place in blast furnaces, 

 since carbon reduces all oxyds of iron at a high temperature. It must 

 then be admitted that granite, gneiss, and diorite, did not contain 

 graphite Avhen the mineral elements of these rocks, such as mica, 

 hornblende, and other ferrous silicates were in a state of fusion. 

 Graphite, then, must have been subsequently introduced into these 

 rocks, but when, and how? Questions such as these are very diffi- 

 cult to answer satisfactorily. The most plausible hypothesis is that 

 graphite has been introduced by the wet way into the crystalline rocks 

 and substituted for one of the mineral components. Thus, in the 

 gneiss of Passau (Bavaria) , it takes the place of mica. 



Graphite is frequently to be met with in granulated limestone, a 

 fact particularly interesting to geologists. Is limestone a product of 

 eruption, or is it a sediment transformed by the action of heat? The 

 presence of graphite is explicable by neither hypothesis. For at a 

 certain temperature, which need not be very high, carbon decom- 

 poses carbonate of lime. This salt may no doubt, under strong 

 pressure, be heated to the melting point without losing its carbonic 

 acid ; this is a laboratory experiment often cited by the Plutonists. 

 But it is quite a different thing with a mixture of carbon and carbon- 

 ate of lime at a high temperature. If we reject the Xeptunian origin 

 of granulated limestone", we must then, as with crystalline rocks, sup- 

 pose that graphite has been introduced by the wet way at a more 

 recent period. The same remark applies to magnetic pyrites (sul- 

 phide of iron), often very rich in plumbago kerns. 



Does graphite, like all carbon, belong to the organic kingdom? It 

 is certain that anthracite, lignite, and coal, arc the result of the slow 

 decomposition of an enormous quantity of vegetables ; the impressions 

 found on them often indicate the kind of vegetables, most of them 

 extinct, which have contributed to these carbonaceous formations. 

 Graphite, if not formed in precisely the same way as coal and 

 anthracite, nevertheless bears signs of an organic origin. The forma- 

 tion of nuclei and veins of graphite in crystalline rocks is sufficiently 

 explained by the decomposition of carbonized hydrogen gas at a high 

 temperature ; this gas, disengaged from organic matters, and penetrat- 

 ing the fissures of the burning rock, Avould und<?rgo decomposition 

 into hydrogen and carbon. 



It is this deposited carbon which forms graphite. If in our labo- 

 ratories we do not obtain exactly the same product, it must be 

 remembered that Nature lias means at her command which escape our 

 researches. We find it impossible to make coal from wood. The 

 wood may be carbonized by the dry or by the wet way. In the first 

 place the carbonization is very rapid ; in the latter it is extremely 

 slow, as is shown by the blackened points of piling sunk in water. 



Finally, graphite has been found in meteorites or aerolites. At- 

 tempts have been made to explain its presence here by the continuance 

 of these stones in soil more or less rich in carbonized principles. But 

 with regard to newly-fallen stones, this explanation is inadmissible. 



