The geological work of Mosses and Alga. — Weed. 49 
stress has been laid upon the geological work performed by ani- 
mals, particularly the molluscs and corals, the magnitude and im- 
portance of a similiar work performed by the humble members of 
the vegetable kingdom have not been fully appreciated. 
It is with the hope of emphasizing the importance or this geo- 
logical work of plants, by alluding to such facts as are already 
known, and describing several new features of the work, that the 
present paper has been prepared. 
So far as known, the mineral-producing plants are all moisture- 
loving or aquatic species and belong to the mosses and the algae, the 
onty exceptions being a few lime-incrusted species of higher orders. 
According as the mineral matter is abstracted by physiological 
processes, to build up the plant structure, or is a strictly chemical 
deposit resulting from reactions engendered by the growth and 
activity of the plants, the deposits may be direct, or indirect in 
their origin. B3- far the greater number of the deposits now 
known belong to the former class and in this case whether the beds 
are formed of stony masses of plant structures in situ, or result 
from an aggregation of isolated plant forms, it is the chemical 
work performed by the vegetation in the abstraction and segrega- 
tion of mineral matter, to which geological interest attaches. 
Besides the familiar and universal storage of carbon in the tis- 
sues of plants and the beds of peat, lignite and coal formed of 
plant remains, the deposits heretofore known to be produced In- 
vegetable life include only the limestones formed by marine algae, 
certain travertine deposits and the beds of diatomaceous earth 
found in Tertiary and more recent formations. To these we may 
add deposits of silica and sesquioxide of iron, formed both by 
mosses and by algae, siliceous sinter and sulphate of lime. 
It has long been known that certain marine algae, particularly 
the corallines and nullipores, possess the power of secreting the 
carbonate of lime, which the}' extract from sea water and of which 
they build their cell walls or strengthen their structures. Such 
plants have been recognized as important aids in the formation 
of the limestones and the banks of calcareous sand s<> character- 
istic of tropical seas. Agassiz has described limestones found on 
the coasts of Florida that consist essentially of the remains of 
these stony alga-. 
It is now known (hat certain fresh water algae and several 
4 
