52 
MOSSES 
ber of species^ is but an imperfect indication 
of the actual number of specimens. 
The mode of preservation differs between 
the mineralization of a solid substance^ as 
coal^ or limestone, to the scarcely altered 
condition of the leaf in amber, or of the 
trunk in the peat bog. Sometimes the plant 
is only represented by a tracing of its sur¬ 
face, but most commonly by a cast of the 
whole substance, effected by a gradual 
removal of the organic matter, and the slow 
substitution of inorganic. 
We will commence our catalogue of 
plants with those of simplest form, but be¬ 
fore doing so must state the range of our 
intended researches. The term fossil in¬ 
cludes all substances lifeless and buried; 
but in reference to geology, it is often 
used to describe only the organic remains 
contained in strata not now in process of 
formation, and in this limited sense it 
will be employed in our enumeration of 
the members of the ancient flora. 
I. Two families of the first or flowerless 
class are found fossil; the conferva, small 
moss-like plants growing in the water, and 
