188 FIRST FORMS OF VEGETATION. 
luxuriance, of which their dwarfed modern repre- 
sentatives can give usnoidea. Ifthe Paleozoic was 
the age of Acrogens, the Eozoic may have been that 
of Thallophytes and Anophytes. Gigantic mosses 
and lichens may have been the sole vegetation, 
and may have produced the extensive deposits of 
graphite which exist in the Lower Silurian, and 
which has as yet afforded no remains of land 
plants. To the chemist the presence of graphite, 
or of a metallic sulphide in a rock, affords clear 
evidence of the intervention of organic life ; and 
these indirect evidences are met with even in the 
oldest known stratified rocks. Nay, strange to 
say, the presence of graphite, native iron, and sul- 
phides in most aérolites, discloses the startling 
fact that these bodies come from a region where 
vegetable life has performed a part not unlike 
that which it still plays upon our globe. Professor 
Daubeny has suggested that the former existence 
of vegetable life in the oldest rocks containing 
no fossil remains, or even graphite, iron or sul- 
phurets, may be ascertained by the presence in 
them of phosphoric acid, which is essential to every 
form of life, and which cannot be dissipated by 
any amount of heat or metamorphic action, when 
in a state of combination. The minutest traces 
of this acid in a rock that might otherwise escape 
notice may be detected indirectly by sowing barley 
