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 



