322 FUCOIDES IN THE COAL FORMATIONS. 



We know little indeed of the true forms and nature of fossil Hydrophites. Mere 

 cellular plants as they were, nothing of them has been preserved by fossilization but some 

 moulds or indistinct impressions ; hence the impossibility of discovering peculiar forms of 

 organism, which might be used as reliable specific characters. In looking over the innu- 

 merable remains of Fucoides, which cover some strata of the Chemung of Pennsylvania 

 or of the Waverly sandstone of Ohio, for example, we perceive at first such differences in 

 the shape of these fossils that their .separation into groups appears an easy task. But in 

 time, when these remains are more thoroughly studied, the gaps are filled by so many 

 intermediate forms that the whole fields of this vegetation of old appears like a grass-plot, 

 each blade of which has some peculiar feature, but none marked enough to make it posi- 

 tively distinct. Therefore we are led to admit, either that there are nearly as many spe- 

 cies as individuals, or only one species, represented by a great number of closely allied 

 varieties. Of course the impossibility of separating these fossil remains into well-charac- 

 terized groups renders them unavailable as geological guides. 



This difficulty is not met with in the study of the fossil coal plants. For, like the acro- 

 genous vegetables of our time, a class to which they mostly belong, they have woody tissue 

 and vessels as constituents of their stems and foliage, and thus generally preserve their es- 

 sential forms, in the process of mineralization, at least under certain circumstances. The 

 leaves are not only well defined in outline, but their surface is generally marked by a dis- 

 tinct system of nervation, peculiar to most of the species. Some of these may be followed 

 and studied in the development of leaves, branches, trunks, and even fruits, the trunks 

 being recognizable by peculiar cicatrices on the bark, and the fructifications being some- 

 times found attached to the plants to which they belong. Hence, if the generic and specific 

 characters of these plants cannot be established on a true scientific basis, they are never- 

 theless evident enough to allow an identification of the remains found in connection with 

 the beds of coal, and thus to permit a reliable comparison in their distribution, or to fix the 

 peculiar horizon where groups of these plants may belong. 



On the other hand, marine plants, like every other kind of vegetable, are apt to 

 modify their shape or to vary according to influences affecting the medium in which they 

 live. In the palaeozoic times the temperature of the sea was regulated rather by the heat 

 of the earth than by atmospheric action, and thus was scarcely variable. The same forms 

 of life could therefore be preserved in this medium for a great length of time, longer 

 indeed in the vegetable than in the animal world, for the life of plants is not in water 

 exposed to destructive accidents, like that of animals. And in its proceeding and re- 



* Prof. James Hall, with remarkable foresight, obtained through his intimate acquaintance with the distribu- 

 tion of the Palaeozoic fossils, remarks in his report (loc. cit. p. 83) that species of Fucoides of the group of the 

 Cauda-yalli might perhaps be found in the Lower Coal Measures of Pennsylvania. 



