INTRODUCTION. 3 
laying the electric telegraph cable between Ireland 
and Newfoundland, that the floor of the Atlantic 
is paved many feet deep with their silicious shields, 
preserving in all their integrity their wonderful 
shapes, notwithstanding their extreme delicacy and 
minuteness, and the enormous pressure of the vast 
body of water which rests above them. Such is 
the wide space which these organisms occupy in 
the fields of nature—a prominence which is surely 
sufficient to redeem them from the charge of in- 
significance, They are inferior in majesty of form 
to palms and oaks, but in their united influence it 
is not too extravagant to say that they are not less 
important than the great forests of the world. 
This vast profusion of minute and humble vege- 
table life serves the obvious purpose of preparing 
the way for higher orders of vegetation. Nature 
is incessantly working out vast ends by humble 
and scarcely recognisable means. The features 
of the earth are being continually altered by the 
germination and dispersion of the algz, mosses, 
and lichens. Bare and sterile mountains are 
clothed with verdure; rocks are mouldering into 
soil; seas are filling up; rivers and streams are 
continually shifting their outlines; and lakes are 
converted into fertile meadows and the sites of 
luxuriant forests, by means of the vast armies of 
Nature’s pioneers. Hard inorganic matters are re- 
