DEVONIAN AND CARBONIFEROUS 291 



With our present knowledge of the Middle Devonian fauna of the 

 Yukon section, a A^ery close relationship to other faunas can not 'oe 

 pointed out. It appears probable, however, that the Devonian fauna of 

 the Yukon Eiver district bears a closer relationship to the Mackenzie 

 River fauna"- than to any of the other western faunas outside of Alaska. 



The known Upper Devonian fauna of the Yukon section, limited as it 

 is to a very few species, is too imperfectly known to afford much basis for 

 comparison with faunas elsewhere. The presence in it, however, of 

 Lieorliynchus and a Buckiola closely allied to if not identical witli 

 retrostriata suggests that a more complete knowledge of it will show a 

 rather close relationship with the Upper Devonian of eastern America. 

 None of the species occurring in the Upper Devonian of the Yukon sec- 

 tion have been thus far found in the Upper Devonian of southeastern 

 Alaska. 



GARB ONIFERO US 



The Devonian rocks are not separated by any break from the overlying 

 Carboniferous terrains. The division line between the two systems lies 

 within the upward extension of the black argillites, which form the 

 uppermost member of the Devonian. As there is no abrupt change in 

 lithologic character in passing from one group to the other, the line of 

 cleavage between the Carboniferous and Devonian must be determined 

 largely on paleontologic evidence. This is as would be expected, for both 

 the uppermost part of the Devonian and the lowest member of the Car- 

 boniferous are represented by sediments that are deposits of deep-sea 

 conditions. 



The Carboniferous terrains of the upper Yukon include about 5,000 

 feet of strata, the lowest of which rest conformably on the Devonian. A 

 triple sulxlivision has been recognized, the two lowest of which form well 

 defined stratigraphic units and have been given formation names, while 

 the upper, which is to be correlated with so-called "Permian" of Alaska, 

 has not been named, because its limits are not well defined. The large 

 collections made from the highest member by the writers are referred by 

 Doctor Girty to the Upper Carboniferous and not to the Permian, as lias 

 been done with other collections from this locality by previous investiga- 



»= F. B. Meek : Remarks on the geology of the valley of the Mackenzie river, with fig- 

 ures and descriptions of fossils from that region, in the Museum of the Smithsonian 

 Institution, chiefly collected by the late Robert Kennicott, Esq. Transactions of the 

 Chicago Academy of Science, vol. 1, 1869, pp. 61-114, pis. xi-xv. 



.1. F. Whiteaves : The fossils of the Devonian rocks of the Mackenzie River basin. 

 Contributions to Canadian Paleontology, vols, i and iii, 1891, pp. 197-253, pis. 27-32. 



