66 R' W. Chancy 



into the Miocene. There is no great break in passing from one to the 

 other when we compare them over many latitudes, and but litde 

 change beyond that brought about by altered temperature or migra- 

 tion. But if Tertiary floras of different ages are met with in one area, 

 great changes on the contrary are seen, and these are mainly due to 

 progressive modifications in climate, and to altered distribution of 

 land. From Middle Eocene to Miocene the heat imperceptibly dimin- 

 ished. Imperceptibly, too, the tropical members of the flora dis- 

 appeared; that is to say, they migrated, for most of their types, I 

 think, actually survive at the present day, many but very slighdy 

 altered. Then the sub-tropical members decreased, and the temperate 

 forms, never quite absent even in the Middle Eocene, preponde- 

 rated. As decreasing temperature drove the tropical forms south, 

 the more northern must have pressed closely upon them. The 

 Northern Eocene, or the temperate floras of that period, must have 

 pushed, from their home in the far north, more and more south as 

 climates chilled, and at least, in the Miocene time, occupied our 

 latitudes. The relative preponderance of these elements, I believe, 

 will assist in determining the age of Tertiary deposits in Europe, 

 more than any minute comparisons of species. Thus it is useless to 

 seek in the Arctic Regions for Eocene floras, as we know them in 

 our latitudes, for during the Tertiary period the climatic conditions 

 of the earth did not permit their growth there. Arctic fossil floras of 

 temperate, and therefore Miocene aspect, are in all probability of 

 Eocene age, and what has been recognized in them as a newer or 

 Miocene f acies is due to their having been first studied in Europe in 

 latitudes which only became fitted for them in Miocene times. 



When stratigraphical evidence is absent or inconclusive, this un- 

 expected persistence of plant types or species throughout the Terti- 

 aries should be remembered, and the degrees of latitude in which 

 they are found should be well considered before conclusions are 

 published respecting their relative age. 



In response to physical changes controlled apparently by emer- 

 gence with its resultant modification of ocean currents, and 

 by mountain-making with its resultant modification of atmos- 

 pheric circulation, a temperate forest came to occupy the lower 



