"When Palæozoic 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 (_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 comparatively unaltered specimens from the coal-formation.[19] 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 slicken-sided laminæ, much like those of some bituminous shales and coarse coals; and in these there 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 Grenville series of Canada, though they certainly underlie the Cambrian series of the St. John or Acadian group, and are separated from it by beds having the character of the Huronian, and thus come, approximately at least, into the same geological position. [Footnote 19: "Acadian Geology," p. 535. In calcified specimens the structures remain in the graphite after decalcification by an acid.] "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 have been found. It is possible, however, that in the Laurentian period the vegetation of the land may have consisted wholly of cellular plants, as, for example, mosses and lichens; and if so, there would be comparatively little hope of the distinct preservation of their forms or tissues, or of our being able to distinguish the remains of land-plants from those of Algæ. The only apparent plant of the Laurentian to which a name has been given, _Archæophyton_ of Britton, from New Jersey, consists of ribbon-like strips, destitute of apparent structure, and which, if they are of vegetable origin, may have belonged to either of the leading divisions of the vegetable kingdom. I have found similar flat frond-like objects in the limestone of the Grenville series, at Lachute, in Canada.