HOW THE ANCIENT FORESTS BECAME COAL. 57 



and sandstones, so as to show that there was nothing universal in the 

 phenomenon, and that it was liahle to interruption by physical changes. 

 It is also easy to conceive that the formation of coal could not have 

 gone on unless the vegetation was adapted to the process 3 and the con- 

 ditions of the climate were suitable. The coal-plants could never have 

 grown and flourished as they did in the present climates of the North ; 

 and our hard-wood trees, with their firm foundations in the ground, 

 and their slow, periodical growth, could never by decaying in the 

 open air have produced the peculiar and rich combinations we find in 

 the coal-beds. The nature and bearing of these three concurrent fac- 

 tors have been carefully studied out by M. L. Grand' Eury, who has 

 for that purpose spent many years in personal inspection of various 

 mines and their surroundings, and has presented, in bis " Memoire sur 

 la formation de la houille " (" Memoir on the Formation of Coal," Paris, 

 1882), a complete theory on the subject, including a review of the de- 

 tails of the process as taught by his observations of the phenomena. 



The plants of the coal-measures, so far as their nature has been re- 

 vealed to us by their remains, were great ferns, gigantic lycopodiums, 

 called by the geologists lepidodendrons, and calamites and asterophyl- 

 lites, allied to existing Equisetacem / all referable to the class of cryp- 

 togams. Besides these was another group, the character of which was 

 long problematical, composed of the sigillarias and stigmarias. It now 

 appears to be established that the stigmarias were a kind of rhizoma 

 which had the faculty of persisting for a long time under the mud un- 

 changed, growing and multiplying by stolons, but incapable in that 

 condition of producing sexual organs ; while under favorable circum- 

 stances they formed enormous buds whence shot up to the height of 

 a hundred or a hundred and fifty feet the huge leaf-clad stems 

 whose fossils, marked with the beautiful scars representing the leaf- 

 attachments, have been called sigillarias. Gymnosperms were also 

 quite plentiful, of one class of which, the cordaites, M. Grand' Eury 

 has made some happy restorations. He has found their leaves and 

 seeds in considerable abundance at Saint-Etienne, and he has observed 

 at the same place visible traces of their carbonized trunks, still stand- 

 ing erect and traversing the sandstone strata of some of the quarries. 



A peculiar feature of these plants was the extraordinary predomi- 

 nance of the cellular or succulent tissues in them, and the correspond- 

 ing rarity of the hard or fibro-ligneous parts, which appear reduced to 

 insignificant cylinders. It was certainly not the destiny of these parts 

 to increase with time, after the manner of the wood of our trees ; and, 

 in examining the mature stems of the ancient plants, we never find 

 any more than an extremely thin ring of real wood. The rest is all 

 pith, and even the bark, except on the outside, frequently presents an 

 open or spongy texture. Such structure is similar to that of the 

 aquatic plants of the present time, which can not exist at all in the 

 air, and wither as soon as they are taken out of the water. An atmos- 



