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 Paleozoic rocks. 
With the 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 ina 
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. Paleopteris, 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 Marattiacez, an order which at present is repre- 
sented by a small number of tropical species which are 
