THE DEVONIAN PERIOD. 491 



III. The Land Life. 



It is not possible to follow the evolution of the land life with even 

 such partial continuity as has been attempted with the marine life, 

 for the record is much more imperfect and its interpretation more 

 uncertain. The known life consisted of land plants, a few snails, 

 insects, myriapods and scorpions, and mere traces of amphibians. 



The land plants. — The dominant element, and the basal one as 

 well, was the vegetation; but there are good reasons to think that 

 its preservation was relatively the poorest. In the early stages of 

 its evolution, vegetation was doubtless more perishable than later, 

 from having acquired less mineral stiffening and less protective inves- 

 titure of bark, husks, nut-shells, and other less perishable parts; but 

 even in their best estate, plant tissues are less well fitted for fossiliza- 

 tion than the shells and skeletons of animals. To this, very adverse 

 terrestrial conditions are added. The normal fate of upland plants 

 is to perish where they grow, and their fossilization is usually pro- 

 hibited by the constant denudation of the surface. If any part of 

 an upland plant escapes its normal fate, it undergoes usually various 

 contingencies of decay, consumption, combustion, and other forms 

 of destruction, before it reaches a place of sedimentation. If, escap- 

 ing these, it reaches a lake or the sea, its lightness tends to keep it 

 afloat and render it peculiarly susceptible to shore action and to differ- 

 ent forms of organic attack. If it survives these, it is liable to be 

 buried near the shore where subsequent denudation is most likely 

 to cut it away, for the extreme borders of nearly all strata, except 

 in cases of unconformable overlap, are denuded. 



In the case of lowland vegetation the chances of prompt burial 

 and preservation are much better, but even here the contingencies of 

 subsequent denudation are large. It is only when the area of sedi- 

 mentation is creeping out upon the land with relatively little shore 

 cutting, or the low lands are undergoing permanent aggradation, that 

 the conditions for the fossilization of land vegetation are even fairly 

 favorable. Even when preserved, the parts of a plant are apt to be 

 dissevered, and their re-assemblage and interpretation is difficult. 

 It is rare that leaves, fruit, twigs, limbs, trunk, and roots are all retained 

 together. In the case of ancient forms, especially where not closely 

 analogous to modern types, it is more or less hazardous to attempt 



