LAURENTIAN AND EARLY PALJIOZOIC. 



15 



When palaeozoic land-plants have been con verted 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 {Dadoxylon 

 Ouangondianum) 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 com- 

 paratively 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 are occasional small pyritous 

 masses which show hollow carbonaceous 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 Lau- 

 rentian of Canada, though they certainly underlie the 

 Primordial series of the Acadian group, and are' sepa- 

 rated from it by beds having the character of the Hu- 

 ronian. 



There is thus no absolute impossibility that distinct 

 organic tissues may be found in the Laurentian graphite, 

 if formed from land-plants, more especially if any plants 

 existed at that time having true woody or vascular tissues ; 

 but it cannot with certainty be affirmed that such tissues 



* " Acadian Geology," p. 535, In calcified specimens th§ structures 

 remain in the graphite after decalcification by an acid. 



