So R. W. Chancy 



as a result of a progressive trend toward cooling and aridity since 

 the early Tertiary, but secondary movements in the opposite 

 direction have been detected and have played their part in estab- 

 lishing the character of modern vegetation. The gradual shifting 

 southward of the northern limits of most of the Eocene species 

 has resulted in their restriction to the low latitudes of Asia and 

 America, in the forests of which there is a remarkable corre- 

 spondence of genera on both sides of the Pacific. Following 

 closely behind them, as successful competitors under changing 

 conditions of climate, the temperate Miocene flora with its 

 dominant Sequoia element left the northern regions and became 

 widely established in middle latitudes of both continents. Further 

 modifications have served to eliminate the redwood from most 

 of its former range and have localized the deciduous element on 

 the eastern sides of the continents where summer rains and 

 \ winter cold are prevalent, or to the higher altitudes of western 

 America where this general climate is duplicated. With the late 

 Tertiary uplift of the Cascade Range and the Sierra Nevada to 

 essentially their present height, and with the consequent devel- 

 opment of diversified topography of high relief, the relatively 

 uniform floras of middle Tertiary time have also become diversi- 

 fied, with major differences on either side of the mountain 

 ranges, and with the various minor differences which are appar- 

 ent in the modern vegetation. A modified type of Miocene forest 

 has migrated as far south as southern Guatemala, where such 

 genera as Alnus, Arbutus, Crataegus, Cupressus, Myrica, Ostrya, 

 Pinus, Prunus, Quercus, and Salix occupy the highlands above 

 the subtropical vegetation of the lower slopes, thus duplicating 

 the association of these two climatic types which characterized 

 the older Tertiary in Oregon and California some 2500 miles to 

 the northwest. 



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