LIFE IN THE PAST 175 
slender, leaflike branches and its club-shaped spore- 
bearing body, is a modern degenerate descendant of 
the treelike calamites of the Carboniferous forest. A 
creeping evergreen, known by the name of clubmoss, 
is in like manner the modern degenerate remnant of 
the scalestem and sealstcm, which were the great trees 
of the forests of the coal period. 
All over the surface of the marsh, between these 
big trees, grew the ferns. While the coal itself was 
formed generally from the scalestems and sealstems, 
the most common fossils found in the shales that lie 
upon the coal beds are the ferns which covered the 
surface of the marsh. 
It is believed by many geologists that this great 
luxuriant forest points to a time when the climate 
was far warmer than it is to-day, when the air was 
moist and heavily laden with carbon dioxide, and 
when a great mass of clouds practically enveloped the 
earth. In this way only do most geologists account 
for the enormous wealth of vegetation in the Car- 
boniferous period and for the abundance of plants up 
to the Arctic Ocean, of the kinds that now grow 
chiefly in the tropics. But of recent years a few 
geologists point to the fact that the peat bogs of to- 
day, which seem to be the beginnings of future coal 
deposits, are found almost entirely in cold countries. 
Hence it is a serious matter to attempt to describe 
