4 Art. 8. — A. Kryshtofovicli : 



forms, the undoubtedly Cretaceous species being included among 

 the Tertiary ones, for example a Nllssonia, which is a characteristic 

 Mesozoic representative. 



Although some bulky collections of plant fossils were made 

 afterwards in the whole of Eussian Sakhalin, during 1908-1910, 

 by N. TiKHONOViCH and P. Polevoi, nothing new has been pub- 

 lished about them, all being left untouched and consequently not 

 made use of in their scheme of stratygraphy.^^ This lack of in- 

 vestigation necessitated a more careful study in situ, for wliich I 

 was specially dispatched by our Eussian Geological Survey in 1917. 



A little before, Mr. Polevoi put at my disposal a few remains 

 of the plants, found in a collection in Petrograd. A glance at 

 these plant impressions raised my suspicion about the correctness 

 of age- determination of the older Dui Series and the Mgach Series 

 believed to be younger, for the fossils from Mgach really looked 

 just as old as the plant remains from Pilevo, correctly taken 

 as Cretaceous by Polevoi. But the authority of the great paleo- 

 botanist Heer and the actual presence of true Tertiary plants in 

 collections from Mgach elaborated by him did not allow me to 

 make such a considerable change in the dominating views about 

 the age of the Mgach flora. However, in our first trip to the 

 environs of Alexandrofsk we collected, in strata hitherto believed 

 to be Tertiary, true Cretaceous plants alhed to those found in the 

 Dakota Series. We were thus convinced of the quite unexpected 

 presence of a Cretaceous flora of a considerably low horizon in 

 Sakhalin. The coflections made by Mr. Polevoi, Miss Stadnichenko 

 and myself in the littoral outcrop of Mgach also proved the occur- 

 rence of a Cretaceous flora, but in the upper parts of the same 

 cliffs and also in the coal bearing beds of the Mgach coal mine, 



1) TiRHoNOYiCH and Polevoi (1915), 



