GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION 223 



throw any light upon the origin of these puzzling organ- 

 isms. 



While it is reasonable to suppose that both liver- 

 worts and mosses existed at a very early period, their 

 great delicacy has prevented their preservation as fossils 

 except in a few cases, and these are all in the later for- 

 mations. No certain remains of Bryophytes are known 

 from the Palaeozoic rocks. 



With tRe Pteridophytes the case is very different. 

 From the Devonian, and possibly still lower, their re- 

 mains occur in great profusion, especially in the Car- 

 boniferous rocks, where they form the predominant type 

 of vegetation, and their remains are often preserved in a 

 most perfect manner, even the inner structure often 

 being so clear as to make a comparison with the tissues 

 of the living forms an easy matter. 



The earliest remains attributed to the ferns occur in 

 the lower Silurian rocks, where a fossil named Eopteris 

 has been found. It is doubtful, however, whether this 

 really is a fern. In the Devonian, undoubted ferns 

 occur. Some of these, e.g. Palseopteris, are admirably 

 preserved so far as the leaves are concerned, and some 

 traces of sporangia have been detected, but these are too 

 imperfect to make clear the affinity of the plant with 

 modern types. 



It is in the coal measures that the most numerous 

 remains of ferns are found, and many of these are in a 

 remarkably perfect state of preservation. The most 

 recent study of these Carboniferous ferns shows that most 

 of them are eusporangiate, and evidently related to the 

 living Marattiacese, an order which at present is I'epre- 

 sented by a small number of tropical species which are 



