FRESH-WATER ALG. 237 
alarming appearances are produced, and then 
only in obscure and isolated localities; but their 
seeds lie around us in immense profusion, waiting 
but the recurrence of similar atmospheric con- 
ditions as existed in former times, to exhibit as 
extraordinary a development. For all we know 
there may be existing amongst us the germs of 
other forms of life, ready to develop themselves 
into new manifestations of the power and wisdom 
of God, if it should please Him to adapt the vital 
envelope of our globe to the uses of other occu- 
pants. The present chemical condition of the 
air is admirably adapted for the healthy develop- 
ment of the forms of life that now exist in it; 
and so likewise is the water for the organisms 
that pervade it. But who can tell what species 
of plants and animals would succeed the present 
species, were there but the smallest change 
effected in the proportions of the constituents 
of these elements? Geology reveals to us the 
singular fact that, when the air and the water 
were densely impregnated with carbonic gas 
during the coal era, an extraordinary develop- 
ment of the humblest forms of animal and plant 
life was the result. The earth was covered with 
dense forests of ferns and mosses, and the waters 
were peopled with myriads of corallines. And 
were similar conditions of the atmosphere and 
