INTRODUCTION 89 



Shingle beach communities occur along the coast, 

 as at Blakeney, Chesil Beach, etc. 



20. The Origin of Plants and the British 

 Flora. 



If we go back to the time when the very earliest 

 traces of plant life that have been discovered grew on 

 the earth, we are forced to admit that our evidence is 

 at present very incomplete. In Pre-Cambrian beds 

 only graphitic material supplies any data as to what 

 the most primitive plants were like. Even here, we 

 are at a dead loss as to their nature, for the graphite 

 which it is suggested may originally have been formed 

 from plants is a structureless form of carbon. 



Still later the earliest plants are very imperfect. 

 But some have been referred to Algae or Seaweeds. 

 And it seems probable that life, plant as well as 

 animal, began in the sea, for the earliest deposits 

 containing fossils are of marine origin, and there 

 was certainly no true terrestrial flora till much later. 

 Doubtless the present day fresh-water Green Algae 

 are derived from some of the marine Algae, which 

 flourished at the dawn of plant-life on this globe. 



From these Green Algae other types of plants ori- 

 ginated, and gradually the direct line of evolution of 

 the higher plants became established. But as to how 

 and when we are as yet practically in the dark. In 

 the Devonian rocks of America, in particular, higher 

 types are ushered in, such as Horsetail-like types, 



