588 PROCEEDINGS OF BOSTON MEETING. 



4. Bluish sandy slates and shales with a rich Miocene plant flora, interstratified with beds of in- 

 durated gravel, fossil wood and lignilic coal. (Kenai group.) 



5. Metamorphic quartzites and slaty rocks, illustrating the geologic series probably from the 

 Jurassic to the upper Cretaceous, with perhaps part of the lower Eocene. (Chico-Tejon.) 



6. Granite and syenite in massive beds, usually without mica and apparently in most instances 

 forming the "backbone" of the mountain ridges or islands, but occasionally occurring in intru- 

 sive masses. (Shumagin granite.) 



The geologic age of these coal-bearing rocks, from which most of the plants 

 enumerated in this paper came, has usually been regarded as Miocene. Heer, 

 who worked up tlie first considerable collection of plants, referred them unhesi- 

 tatingly to this horizon, and regarded them as the equivalent of the Miocene beds 

 of Greenland, Spitzbergen, the Braunkohl of eastern Prussia and the lower Mo- 

 lasse of Switzerland. . Lesquereux and (at first) Newberry do not appear to have 

 seriously questioned their Miocene age. Of the 73 species enumerated by Lesque- 

 reux in his latest publication on Alaskan plants, 21 are found in Greenland and 

 Spitzbergen and 31 in the Miocene of other parts of the world. These considera- 

 tions show that the fossil flora of Alaska is inseparably connected with that of the 

 Disco island and Atanekerdluk beds of Greenland and the so-called arctic Miocene 

 of Spitzbergen .and Sachalin. Whatever is decided concerning them must apply 

 with equal force to Alaska. 



Mr J. Starkie Gardner appears to have been the first to question the Miocene 

 age of the Greenland beds,* or rather of the Arctic floras in general. The sequence 

 of British Eocene floras is almost unbroken, andin studying them and their rela- 

 tions to the Miocene flora he was led to important conclusions. He says : 



There is no great break in passing from one to the other (Eocene to Miocene) when we compare 

 them over many latitudes, and but little change beyond that brought about by altered tempera- 

 ture or migration. But if Tertiary floras of different ages are met with in one area, great changes, 

 on the contrarj', are seen, and these are mainlj'' due to progressive modifications in climate and to 

 altered distribution of land. Imperceptibly, too, the tropical members of the flora disappeared ; 

 that is to say, tiiey migrated; for most of their types, I think, actually survive at the present daj', 

 many but slightly altered. Then the subtropical members decreased, and the temperate forms, 

 never quite absent even in the middle Eocenes, preponderated. As decreasing tertiperature drove 

 the tropical forms south, the more northern must have pressed more 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 last, 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 use- 

 less 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 

 floras of temperate, and therefore Miocene, aspect are in all probability of Eocene age, and what 

 has been recognized as a newer or Miocene facies is due to their having been first studied in 

 Europe in latitudes which only became fitted for them in Miocene times. 



This change of view as to the age of the so-called Arctic Miocene, as proposed 

 by Gardner, has already received considerable confirmation from American paleo- 

 botanists, and while it can hardly be regarded as settled, it may be accepted as 

 extremely probable. 



Dr J. S. Newberry, in one of his latest publications, said : f 



I called the Fort Union group Miocene because I identified it with the plant-bearing beds of 

 Mackenzie river, Disco island, Greenland, etc, of which the flora had been studied by Professor 



* British Eocene flora, part i, 1879, p. 8. 



t Trans. N. Y. Acad. Sci., vol. ix, p. 1 of reprint. 



