50 Art. 8.— A. Kryshtofovich : 



The true Populus arctica has beea found in Atanekerdluk and in 

 Arctic Canada, both being Tertiary according to Heee. . But already 

 at that time, Marquis Sapouta expressed the opinion about an older 

 age of the Canadian floras, which was strongly supported by 

 Dawson against Heee. Sapoeta's opinion is in full agreement with 

 our recent condition of knowledge and was moreover partly con- 

 firmed by the occurrence of animal fossils. It is very probable, that 

 P. arctica has already been observed in the Cretaceous of America, 

 but treated under some other names, for instance, by Dawson and 

 Newbeeey (1898). But there is no question, about the true Cretace- 

 ous age of this fossil in Mgach. Another and younger horizon, at 

 Cape de la Jonquière, well characterized by its fauna, also bears well 

 preserved specimens of Populus arctica. Consequently, this species, 

 formerly regarded as decidedly Tertiary, must now be introduced 

 into the list of Cretaceous plants. In Sakhalin, namely, it occurs 

 in a flora, older than those elsewhere ; though the age of many 

 other floras believed as Tertiary must be revised. In the Dakota 

 flora, the genus Populus is represented by some other, but allied, 

 species. Populus arctica passes from the Upper Cretaceous of 

 Arctic, right through into the Laramie of America and the Lower 

 Tertiary of the high North. It is very important to remark here 

 in favour of its Cretaceous age rather than the Tertiary, its total 

 absence in the really Tertiary floras of Dui and Mgach (the latter 

 contains Castanea Kuhinyi, Comptoniphyllum cf. japonicum, Po- 

 pulus latior, Carpinus, Alnus etc., which are all characteristic Ter- 

 tiary species). Under this condition, we can well explain the soli- 

 tary position of this species among the recent sections of the genus 

 Populus, while all the other sections of this genus are well repre- 

 sented in really Tertiary floras. The position and distribution of 

 this species among the extinct floras of the whole Holarctic Pro- 

 vince deserves great attention. 



