PRB-CARBONIPEROtIS PLANTS. ^ . 81' 



forms, we might discover in them the prototypes of genera which ascend 

 into the Devonian.* ' 



3. Such views as to a primitive Silurian and Laurentian flora are 

 strengthened by the obvious fact that the plants of the Lower and Middle 

 Devonian have the aspect of the remains of a decaying flora verging on ex- 

 tinction, and pointing backward in Geological time, while those of the Upper 

 Devonian give us a great number of new forms and point onward to the 

 Carboniferous. As already stated the Lower and Middle Erian flora stands 

 by itself in the prevalence of such archaic and prototypal forms as Proto- 

 taxites, Psilophyton, Nematoxylon, and Arthrostigma. Is it probable that 

 it was thus isolated ? Is it not more likely that these plants were the 

 successors of an older and more primitive flora ? 



This is vividly presented to the mind in the Erian Conifers. In the 

 Lower Sandstones of Gasp^ we find numerous trunks of large trees, all 

 having the structure of Protatazites. In the Hamilton Group of New York 

 and in the sandstones of St. John, these are replaced by Dadoxylon, a 

 type extending into the Carboniferous and thence to the modern Araucarian 

 pines. There is no transition from one typo to the other, nor are they 

 intermixed in the same beds. The Middle Devonian would thus seem to 

 have been the grave of Prototaxites and the birth-place of Dadoxylon, in so 

 far as the regions in question are concerned. 



Something of the same kind occurs in the Carboniferous, in the scanty 

 and somewhat antique Lower Carboniferous flora pointing backward to the 

 Upper Devonian, just as the Lower Devonian may be supposed to point 

 backward to the Silurian. 



• Even before the discovery of the first specimens of Eozoon Canadense, and some time 

 before the microscopic investigations of the writer had established the organic character 

 and aflBnities of these fossils, Dr. T. Sterry Hunt had already in the Amer. Jour. Science for 

 May, 1855 (XXV, 436) asserted that " the presence of iron ores, not less than that of gra- 

 phite points to the existence of organic life even during the Laurentian or so-called Azoic 

 period." The same argument is maintained by Dr. Hunt in the Quar. Jour. Geol. Soc. for 

 1859 (p. 403) and the Ainer. Jour. Science for July, 1860 (XXX, 134) while in the last named 

 Journal for May, 1861 (XXXI, 395) he says: " The great processes of deoxydation in nature 

 are dependant upon organization ; plants by solar force convert water and carbonic acid 

 into hydrocarbonaceous substances, from whence bitumens, coal, anthracite and plumbago; 

 , and it is the action of organic matter which reduces sulphates, giving rise to metallic sul- 



phurets and sulphur. In like manner it is by the action of dissolved organic matters that 

 oxide of iron is partially reduced and dissolved from great masses of sediment to be subse- 

 i, quontly accumulated in beds of iron ore. We see in the Laurentian series beds and veins 



of metallic sulphurests, precisely as in more recent formations ; and the extensive beds o 

 iron-ore, hundreds of feet thick, which abound in that ancient system, correspond not only 

 to great volumes of strata deprived of that metal, but, as we may suppose, to organic 

 ""' ' matters, which, but for their oxydation might have formed deposits of mineral carbon far 

 more extensive than those of jilumbago which we actually meet in the Laurentian 

 strata. All these conditions lead us then to conclude the existence of an abundant vege- 

 tation during the Laurentian period. ' 



