FOUR 
THE ERA OF THE FERNS 
E ARLIEST fossil land plants that have been dis¬ 
covered come from the early Devonian period. 
While rock impressions of plants of that age have been 
found in various parts of America and the Arctic, the 
only source of our knowledge of their structure is a 
large bed of petrifacts discovered in 1915 near the 
village of Rhynie in Aberdeenshire, Scotland. A swamp 
seems to have existed there near a seashore in early De¬ 
vonian days, and was exposed to inundations from time 
to time. It also happened that a geyser or some powerful 
mineral spring was located near the swamp and frequently 
soaked it with water containing a high percentage of 
silica. The result was that the plant life of the swamp 
was impregnated with silica, and thus consecutive layers 
of petrifacts were preserved. 
Nowhere else do we find any evidence of the anatomi¬ 
cal structure of early Devonian plants. Two Scotch 
paleobotanists, Kidston and Lang, examined this material 
60 
