THE RED ALG. 9! 
the Silurian period, which have been preserved, can, it is 
true, give us but a faint idea of them, because the material 
of these Algze, like that of most others, is ill-suited for pre- 
servation in a fossil state. As has already been remarked, 
a large portion of coal is perhaps composed of them. 
Less important is the fourth class of Algz, that of the 
Rose-coloured Alge (Rhodophycee), or Red Sea-weeds (Flo- 
ridez). This class, it is true, presents a great number 
of different forms; but most of them are of much smaller 
size than the Brown Alez. Although they are inferior to 
the latter in perfection and differentiation, they far surpass 
them in some other respects. To them belong the most beau- 
tiful and elegant of all Algze, which on account of the fine 
plumose division of their leaf-like bodies, and also on account 
of their pure and delicate red colour, are among the most 
charming of plants. The characteristic red colour some- 
times appears as a deep purple, sometimes as a glowing 
scarlet, sometimes as a delicate rose tint, and may verge 
into violet and bluish purple, or on the other hand into 
brown and green tints of marvellous splendour. Whoever 
has visited one of our sea-coast watering places, must have 
admired the lovely forms of the Floridez, which are fre- 
quently dried on white paper and offered for sale. 
Most of the Red Alge are so delicate, that they are quite 
incapable of being petrified ; this is the case with the splendid 
Ptilotes, Plocamia, Delesseria, etc. However, there are in- 
dividual forms, like the Chondria and Spheerococca, which 
possess a harder thallus, often almost as hard as cartilage, 
and of these fossil remains have been preserved—principally 
in the Silurian, Devonian, and Carboniferous strata, and 
later in the oolites. It is probable that this class also had 
