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profusely imbedded in the rocks, and by the most numerous and richest 

 deposits of bitumen discovered, as yet, by human agency. The forms rec- 

 ognized in the fossil remains indicate a more diversified kind of vegeta- 

 tion, and a more complex and more perfect structure. Some of them 

 have already characters which seem identical with those of more recent 

 fossil species, and even closely allied to some of our time. This corre- 

 lation is explainable in two ways : First, in supposing that, as vegeta- 

 bles have characters in accordance with the surroundings wherein they 

 live, marine plants vary especially according to depth and pressure, to 

 the temperature of the water, and also to its proportion of saline or 

 other mineral elements. All these agents are not subject to modifi- 

 cations either as distinct or as rapid as those which govern the atmos- 

 phere, and therefore the types of the Algse are preserved for a longer 

 time less diversified and more widely distributed than those of the land- 

 plants. On another side, the difficulty of exact determination of fossil 

 Algae may be taken into account for explaiuiug the cases of identity as 

 merely apparent, the more important characters of those plants being 

 more or less undiscernible in a fossil state. The evidence of land veg- 

 etation is seen at the base of the Devonian, in fossil remains of Lycopo- 

 diaceous species, whose size is about the same as that of the larger club- 

 mosses of our woods. They belong to the genus Psilophytum, estab- 

 lished by Professor Dawson, of Canada, and evidently bear the characters 

 of the club-moss family ; branches unfolding like those of the ferns, by 

 unrolling (circiuate) ; stems dividing alternately by the forking, and 

 bearing both upon their own bark and that of their creeping rhizomas, 

 the scars or the marking of the point of attachment of the leaves. To 

 this genus belongs one of the Silurian species mentioned above. Most 

 of the fossil plants of this family are characterized and identified by the 

 form and the position of these scars, which, though generally round upon 

 the rhizomas, are rhomboidal and diversified indeed upon the stems. 

 Originally, or when seen upon young branches wherefrom the leaves 

 have been recently detached, these scars are small, scarcely the sixteenth 

 of an inch in diameter; they increase, however, rapidly in size, pro- 

 portionally to the enlarging of the stem, and upon large trunks measure 

 sometimes one and a half inches in diameter. In the oldest and more 

 remarkable order of this family, that of the Lepidodendrce, the scars 

 are generally contiguous and in spiral order. In another, that of the 

 Sigillarke, they are more generally placed in vertical series and at a 

 distance from each other. 



From the Lower Devonian, the predominance of land-plants becomes 

 gradually more marked in ascending, but rather by the increasing size 

 of the representatives than by their number. A few stems of Lepido- 

 dendron are recorded from the Middle Devonian. In the upper part, the 

 remains of laud-plants become of more frequent occurrence, and repre- 

 sent already all the vegetable divisions recognized in the subsequent 

 jieriod, that of the Carboniferous, and even more ; for in the United 

 States^ at least, the Chemung Period has, in the Lycopodiacece, species of 

 Lepidodendron and of iSigillaria ; species of Calamites representing the 

 Uquisetacece family, a considerable number of ferns, already some of 

 them typically allied to those of the coal, and a few species of uncertain 

 relation, FlabeUaria and NoeggeratMa, known by long, striated, ribbon- 

 like leaves, which have been considered as representing a family of 

 vegetables intermediate between the Lycopodiacecv and the Cycadcu ; 

 and it has also, which is more remarkable in considering the vegetable 

 scale of distribution, large trunks of fossilized and solidified wood, rec- 

 ognized by its structure as representatives of a genus of Conifers, the 



