18 THE CANADIAN NATURALIST. ' [March 



stones derived from the metamorphosis of such rocks no organic 

 structure remains. It is true that, in certain bituminous shales 

 and limestones of the Silurian system, shreds of organic issue can 

 sometimes be detected, and in some cases, as in the Lower Silurian 

 limestone of the La (cloche mountains in Canada, the pores of 

 brachiopodous shells and the cells of corals have been penetrated 

 by black bituminous matter, forming what may be regarded as 

 natural injections, sometimes of much beauty. In correspondence 

 with this, while in some Laurentian graphitic rocks, as, for 

 instance, in the compact graphite of Clarendon, the carbon presents 

 a curdled appearance due to segregation, and precisely similar to 

 that of the bitumen in more modern bituminous rocks, I can 

 detect in the graphitic limestone occasional fibrous structures 

 which may be remains of plants, and in some specimens vermicular 

 lines, which I believe to be tubes of Eozoon penetrated by matter 

 once bituminous, but now in the state of graphite. 



When palaeozoic land-plants have been converted into graphite, 

 they sometimes perfectly retain their structure. Mineral charcoal, 

 with structure, exists in the graphitic coal of Rhode Island. The 

 fronds of ferns, with their minutest veins perfect, are preserved 

 in the Devonian shales of St. John, in the state of graphite; and 

 in the same formation there are trunks of Conifers (^Dadoxijlon 

 onangondianum) in which the material of the cell-walls has been 

 converted into graphite, while their cavities have been filled with 

 calcareous spar and quartz, the finest structures being preserved 

 quite as well as in comparatively unaltered specimens from the 

 coal-formation.* No structures so perfect have as yet been 

 detected in the Laurentian, though in the largest of the three 

 graphitic beds at St. John there appear to be fibrous structures, 

 which I believe may indicate the existence of land-plants. This 

 graphite is composed of contorted and slickensided laminae, much 

 like those of some bituminous shales and coarse coals ; and in these 

 there are occasional small pyritous masses which show hollow car- 

 bonaceous fibres, in some cases presenting obscure indications of 

 lateral pores. I regard these indications, however, as uncertain ; and 

 it is not as yet fully ascertained that these beds at St. John are on 

 the same geological horizon with the Lower Laurentian of Canada, 

 though they certainly underlie the Primordial series of the A.cadian 



' " Acadian Geology," p. 535. In calcified specimens the structures 

 remain in the graphite after decalcification by an acid. 



