794 



THE POPULAR SCIENCE MONTHLY. 



tic of the oldest Erian beds. The specimens which I have seen from 

 New York, from Gaspe, and from Brazil, leave no doubt in my mind 

 that these were really marine plants, and that the form of a spiral 

 frond, assigned to them by Hall, is j)erfectly correct. They must have 

 been very abundant and very graceful plants of the early Erian, im- 

 mediately after the close of the Silurian period. 



It is not surprising that great difficulties have occurred in the de- 

 termination of fossil alga?. Enough, however, remains certain to 

 prove that the old Cambrian and Silurian seas were tenanted with sea- 

 weeds not very dissimilar from those of the present time. It is further 

 probable that some of the graphitic, carbonaceous, and bituminous 





W it 



V, 1/ ^^ j %i^p 





Fio. 6.-S1LUIUAN Vegetation Restored. Profanmdann, Berwynia, Nematophyton, Spherw- 

 phyllum, Artlirostigma, Pnlophyton. 



shales and limestones of the Silurian owe their carbonaceous matters 

 to the decomposition of algaj, though possibly some of it may have 

 been derived from graptolites and other corneous zoophytes. In any 

 case, such microscopic examinations of these shales as I have made, 

 have not produced any evidence of the existence of plants of higher 

 grade, while those of the Erian and Carboniferous periods, similar to 

 the naked eye, abound in such evidence. It is also to be observed 

 that, on the surfaces of beds of sandstone in the Upper Cambrian, 



