A GENERAL SURVEY n 



life first of all appeared on this earth, but there 

 is good reason for believing that it was evinced 

 in the form of minute plants not unlike the 

 microscopic algse which abound everywhere at 

 the present time. These, in company with some 

 of the higher types of non-flowering species, 

 such as hchens and mosses, played an important 

 part in preparing the surface of the world for 

 the advanced forms of vegetation. At this 

 far distant period there was nothing in the way 

 of soil as we know it at the present time. The 

 hard, unbroken rocks could give no roothold, 

 and the only kinds of plants which could hope 

 to live would be those of a comparatively 

 simple type. 



It is possible to get a very good idea of 

 how the surface of the earth has been rendered 

 suitable for growth of all kinds by studying 

 walls. The new wall which has just been built 

 is absolutely sterile — it is a desert in the truest 

 sense of the word. But it is not very long 

 before vegetation begins to put in an appear- 

 ance. After a few weeks of rainy weather the 

 bricks and mortar do not look quite so hideously 

 red and white ; a close examination reveals the 

 fact that in places an actual coating of green 



