24 



sions in 3,000 to 4,000 years, which may be the highest age of living ones. 

 Their long life is undoubtedly due to the fact that they are not liable to at- 

 tacks by insects, fungus, and hardly by fire. , 



While this persistence of life is one of the attributes which in the bat- 

 tle for life must count as of immeasurable advantage, the other characteris- 

 tic of arboreal development, its elevation in height above every living thing, 

 is no less an advantage over all competitiors for light, which is the source 

 of all life ; and in this competition, size must ultimately triumph. 



Endowed with these weapons of defensive and offensive warfare, for- 

 est growth has endeavored, and no doubt to a degree succeeded through all 

 geologic ages, during which the earth supported life, in gaining possession 

 of the earth's surface. 



As terra firma increased, emerging in islands above the ocean, so in- 

 creased the area of the forest, changing in composition, to be sure, with the 

 change of physical and climatic conditions. 



As early as the Devonian age, when but a small part of our continent 

 was formed, the mud flats and sand reefs, ever increasing by new accumu- 

 lations under the action of the waves and currents of the ocean, were 

 changed from a bare and lifeless world above tide-level to one of forest- 

 clad hills and dales with quaint forms, like the tree rushes and the proto- 

 types of our pines, the Dadoxylon. 



The same class of flowerless plants, known as vascular cryptogams, 

 with colossal tree ferns and the Sigillarias added, became more numerous 

 and luxuriant in the Carboniferous age. 



This vegetation probably spread over all the dry land, while other 

 forms made the dense jungle in the marshy places and lakes with floating 

 islands; the thick deposits of vegetable remains from these forests were 

 finally, in the course of geologic revolutions, turned into the great coal 

 fields. 



During these geologic revolutions some of the floral types vanished al- 

 together, and new ones originated, so that, at the end of Mesozoic times, a 

 considerable change in the landscape is noticeable. In addition to conifer- 

 ous trees, the palms appeared and the first of Dicotyledons, such as Oaks, 

 Dogwood, Beech, Poplar, Willow, Sassafras and Tulip tree. Species in- 

 creased in numbers, adapted to all sorts of conditions, the forest in most 

 varied form and luxuriance climbed up the mountain sides to the very 

 crests, and covered the land to the very poles with a flora of tropical and 

 semi-tropical species in profusion, and large mammals roamed over the 

 open spaces. 



Then came the levelling processes and other changes of post- Tertiary 

 or Quaternary times, the glaciation of mountains and nothern latitudes, 

 with the consequent changes of climate, which brought about correspond- 

 ing changes in the ranks of the forest, killing out many species around the 



