50 



THE THEORY OF EVOLUTION 



organisms under water. For this reason land dwellers 



o 



rarely become fossilized. 



For the investigation of the old-world fauna this 

 circumstance is less serious than for the flora, since 

 the greater number of the animals are and were 

 inhabitants of the water and par- 

 ticularly of the ocean. But of the 

 higher plants l which inhabited the 

 sea we know nothing. 



Hence it happens that formations 

 which are exclusively marine and, 

 particularly for our present inquiry, 

 very important stratifications the 

 pre- Cambrian, Cambrian, Silurian, 

 Mussel Chalk, and others only now 

 and then offer examples of sub- 

 merged land plants. With regard 

 to the flora we gather exact data 

 only from those periods and regions 

 where extensive areas of land were 

 marshy or, owing to great aerial 

 humidity, were covered with forests. Only under such 

 circumstances were the conditions existent for such 

 processes as led to the formation of the coal seams, in 

 which we find entire generations of successive growths, 3 

 and these in the best condition. It must also be 

 considered that none of the primeval plants have 



' Higher plants ' we only accept temporarily in the sense of their 

 higher systematic position, as they are recognized generally by botanists. 



2 H. Potonie: Die Entstehung der Steinkohle und der Kaustobiolithe 

 uberhaupt, Berlin, 1910. 



FIG. 10. SECTIONS OF 



BEECH. 



a, with bark ; b, with 

 bark removed show- 

 ing bast ; c, with bast 

 removed to true 

 wood. (After GolJian. ) 



