423 
the original surface. That such a change has been produced, and 
that the cortical part of these plants was much thicker than any of 
the succulent plants now known, is evinced in numerous specimens. 
So different, indeed, do these plants appear to have been from any 
vegetable now known, as to give full reason for supposing them to 
have belonged to a tribe entirely lost. 
Every oryctologist is aware of the difficulty of giving names to 
fossil plants, each schistous stratum being an immense herbarium, 
of which every separated schist is a folio, on which are depicted the 
figures of plants of the old world ; most of which it is probable no 
longer exist. Not only is it difficult, with many fossil plants, to 
determine the species and genera in which they should be placed ; 
but frequently it happens, that their appearances differ so much 
from those plants with which we are acquainted, that it is not pos- 
sible even to determine their proper station in the natural order of 
plants. Among the remains of plants of this latter description may 
be mentioned those of which we have been just speaking, the ap- 
pearances of which seem to be such as to defy description. You 
have already observed the avowed inability of Dr. Woodward and 
Mr. Da Costa to form a judgment of their nature, or give a satis- 
factory account of the appearances which they present: a later 
writer, M. Walch, appears to have experienced no less difficulty. 
In onJ specimen of this kind, he remarks, the appearances are such, 
as would have been produced by the feet of a kid, and even suggests 
that the impressions on its surface might have been the track of some 
such animal. 
To particularize all the different known" plants which have been 
supposed, by different authors, to have been seen in a fossil state, 
would employ much more room than can be allotted here for that 
purpose, especially when we are, at the same time, taught how little 
reliance can be placed on the opinions thus given. It is, perhaps, 
sufficient to say, that the fossil plants of Germany have been 
