PLANTS FROM ALASKA. 175 



showing a remarkable resemblance in their forms. The resemblance 

 is such as to suggest land coiuiection in the lower Oolite epoch between 

 Asia and North America and a common flora. 



In Lower Cretaceous times, however, they had become nearly extinct 

 on the American continent, even in those parts where they had been so 

 prominent in the Lower Oolite. In all the Lower Cretaceous floi'a of the 

 northwestern region the only Ginkgo found occurs in the Kootanie beds 

 of Canada. Sii' William Dawson, in his Mesozoir Floras of the Rocky 

 Mountain Region of Canada," describes three fossils which he regai'ds as 

 Ginkgos. One of these, given on pi. ii, fig. 1 , he identifies with (I. sihin'ra 

 Hear; another, shown on pi. ii, fig. 2, he determines as G. Icpiiln Heer; 

 and a third, depicted on pi. ii, fig. 3, he names G. nana. His (/. Ic/iida and 

 G. nana are evidently not Ginkgos, but are probal)ly a Baiera, and l)oth 

 the same species. His Ginkgo sibirica is a true Ginkgo and may be that 

 spocies. It is the sole survivor apparently and is much smaller than 

 most of the types common in the Lower Oolite. \i\ the Alaskan fossils 

 the relative ai)undance of the specimens of the two Ginkgos shows this 

 type of plant is still present in force. The large size of the leaves shows 

 that it is probal)ly still in full vigor. This indicates that the time in 

 which these Ginkgos li\-ed in Alaska is not so late as the Lower Cretaceous. 

 The characteristic Lower Oolitic forms still constitute a large element in 

 the flora. 



The floras of the dift'erent parts of the northern hemisphere in the 

 Lower Oolite and the Wealden are compai'atively well known; the 

 vegetation of the intervening time, especially in its foliage, is little known. 

 It is probable that many of the Jurassic types found in the Wealden or 

 Lower Cretaceous flourished in the Upper Oolite and survived in the 

 Lower Cretaceous. The finding, then, in a locality of such Lower 

 Cretaceous forms asCla(loj)hlebis alata, Onychiopsis psilotoides, Cladophlehis 

 Huttoni, etc., does not necessarily prove a Lower Cretaceous age. 



The age of the formation yielding the Alaskan fossils, as indicated 

 by them, is not older than the Lower Oolite, and not younger than the 

 Lower Cretaceous, but is probably between them. 



"Trans. Roy. Soc. Canada, Sect. IV, Vol. Ill, 188.5, p. 8. 



