General 
because there is no recognised translation of the German 
term “Urboden,” which means land or soil which has 
never been touched or altered by plants). 
In making a tunnel near Glasgow, a layer of almost 
liquid clay had been struck. On a field close by the 
ordinary surface soil had been removed from a few 
square yards and piled up in a long mound, and the 
whitish clay which had been buried deep in the earth 
since some time in the ice age was deposited on the 
vacant space. 
After the work had been stopped, there was an 
extraordinary difference between the flowers on the 
mound of surface soil and those of the “ mineral” clay. 
During two summers scarcely a plant succeeded in 
establishing itself on the clay, and those few that did 
manage to grow did so unhappily and seemed also to 
depend chiefly upon blown dust or accidental patches of 
good earth. On the mounds of surface soil the weeds 
and grasses were extremely luxuriant, and produced a 
rich and flourishing crop in a very short time. 
A freshly cooled lava flow is perhaps the only modern 
representative of what was the condition of the whole 
world before plants had begun to colonise its surface. 
The manner in which such fresh lavas are gradually 
occupied by vegetation is extremely interesting, because 
this process gives us some hint as to how, in the very 
earliest of all geological periods, the plant-world may 
have set about its task. 
The eruption of Krakatoa gave a splendid opportunity 
for such observations ; an entirely clean sweep had been 
made of all living plants and animals: the soil was 
nothing but newly cooled lavas or volcanic ash, 
Dr. Treub found that the first vegetation consisted of 
certain minute blue-green seaweeds. Next came a pro- 
fusion of ferns, and at a later date especially such flower- 
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