FIRE, ICE 



nated. That was unfortunate, for, at that time, Pines, Oaks, 

 Guelder Rose, Willows, as well as Sequoias allied to the 

 Mammoth tree and Sassafras, may have lived in Scotland 

 along with tapirs, opossums, marsupials, and other extra- 

 ordinary beasts. 



When the lava cooled and became trap-rock, it was at once 

 attacked by frost, by wind, and by rain. Then by a very 

 slow process of colonization, vegetation slowly and gradually 

 crept over the trap-rock and rich mould and plant remains 

 accumulated. At a much later date, there was another 

 wholesale destruction. This time, it was the great Ice Sheet 

 coming down from the Highland hills. Probably it drove 

 heavily over the top of Pennell Brae and worked up into fine 

 mud and powder every vestige of the miocene vegetation. 



The very rocks themselves would be scratched, polished, 

 and rounded off. When the glaciers melted away and left 

 the surface free, it would consist of these rounded rocks alter- 

 nating with clay-filled hollows. The trap-rock below would 

 be covered by a subsoil due to particles of trap, of Highland 

 and other mud, with remains of the miocene vegetation. 

 Upon this surface, frost, wind, sunshine, and rain would 

 again begin to perform their work. 



But the subsoil, thus wonderfully formed by fire in the 

 miocene, by frost in the glacial, and by weather in our own 

 geological period, very soon felt the protecting and shelter- 

 ing effect of a plant-covering. 



First a green herb rooted itself every here and there amidst 

 the desolate boulder-clay or perhaps in a crevice where good 

 earth had accumulated. Then the scattered colonists began 

 to form groups ; soon patches of green moss united them. 

 Then a continuous green carpet could be traced over a few 

 yards here and perhaps on a few feet somewhere else. But 



147 



