FERNS, FOSSILS AND FUEL 
causes may bring about the same result. The possibility 
that a variety of processes springing from diverse circum¬ 
stances may lead to the same result is often overlooked, 
when a phenomenon is explained by a single hypothesis. 
The green carpet which spread over the earth from the 
edges of the ocean and the deltas of rivers, and which first 
followed the water-courses and only later rose to the 
highlands, consisted probably of small moss-like plants, 
which were not actually mosses, but only looked like them. 
Among these, there were larger, grass-like plants, not 
true grasses, but resembling them in appearance. With 
the progress of time came larger plants looking much 
like ferns and club-mosses and horsetails of our day. 
Some of these types developed into shrubs, and some 
of the shrubs developed into trees. 
By the beginning of the Devonian period, all these 
forms, including great trees which, though unlike our 
present trees, constituted the prairies and forests of the 
time. The colors of this vegetation were probably green, 
brown, yellow, and black; no striking colors, such as red 
or blue, interrupted the comparative monotony of this 
primitive color scheme. The brighter colors probably 
came much later, and were useful in attracting insects to 
help in the reproductive process by carrying pollen dust 
from one plant to another. 
58 
