16 



THE GEOLOGICAL HISTORY OF PLANTS. 



I' i 



4il 



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 compara- 

 tively 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 AlgaB. 



We may sum up these facts and considerations in the 

 following statements : First, that somewhat obscure 

 traces of organic structure can be detected in the Lauren- 

 tian graphite ; secondly, that the general arrangement 

 and microscopic structure of the substance corresponds 

 with that of the carbonaceous and bituminous matters in 

 marine formations of more modern date ; thirdly, that if 

 the Laurentian graphite has been derived from vegetable 

 matter, it has only undergone a metamorphosis similar in 

 kind to that which organic matter in metamorphosed 

 sediments of later age has experienced ; fourthly, that the 

 association of the graphitic matter with organic lime- 

 stone, beds of iron-ore, and metallic sulphides greatly 

 strengthens the probability of its vegetable origin ; fifthly, 

 that when we consider the immense thickness and extent 

 of the Eozoonal and graphitic limestones and iron-ore 

 deposits of the Laurentian, if we admit the organic origin 

 of the limestone and graphite, we must be prepared to 

 believe that the life of that early period, though it may 

 have existed under lov/ forms, was most copiously devel- 

 oped, and that it equalled, perhaps surpassed, in its re- 

 sults, in the way of geological accumulation, that of any 

 subsequent period. 



Many years ago, at the meeting of the American As- 

 sociation in Albany, the writer was carrying into the 

 room of the Geological Section a mass of fossil wood from 

 the Devonian of Gasp6, when he met the late Professor 

 Agassiz, and remarked that the specimen was the re- 

 mains of a Devonian tree contemporaneous with his 



