PREFACE 



The Great Northwest Forest. 



The presence of such a large number as sixty 

 species of cone-bearing trees in Northwest America, 

 is due, principally, to the fact that they are really 

 natives of more northern or more elevated regions, 

 from which they were expelled ages ago, by the ex- 

 treme cold of the last Ice- Age; which, in turn, 

 retreated before a Thermal Age, during the prevalence 

 of which the plants returned from the southern 

 hemisphere and spread over the temperate plains, or 

 became stranded upon the cool mountains finding 

 homes only where their constitutions and their en- 

 vironment permit the maintenance of life and perpet- 

 uation of their species. 



The great development of these trees into larger 

 forms and bearing larger fruit than trees of any other 



(v) 



