Mat 11, 1906.] 



SCIENCE. 



739 



and sixteen also common to the Jurassic of 

 Siberia, a diSerence whicli will hardly justify 

 conclusions based on numerical grounds alone, 

 as to the probable connection between such 

 regions. Professor Ward nevertheless infers 

 from such evidence, that a definite land con- 

 nection existed in Jurassic time, between Asia 

 and northwestern America, and this opinion 

 is strengthened by reference to the remarkable 

 similarity with respect to number and kinds, 

 of the types of Ginkgo found both in Siberia 

 and Oregon. In this connection, however, it 

 is instructive to recall the conclusions of Asa 

 Gray with respect to similar relations as ex- 

 hibited by the existing floras of the three 

 regions mentioned. 



From a study of Japanese plants collected 

 by the Perry Expedition in 1852-1854, sup- 

 plemented by subsequent collections, he found 

 that out of a total of 580 Japanese plants, 

 about 120 also occurred in western North 

 America; 134 in eastern North America, and 

 157 in Europe. A further analysis of these 

 relations showed that ' there has been a pecul- 

 iar intermingling of the eastern American and 

 eastern Asian floras, which demands explana- 

 tion ' ; but upon a critical examination of the 

 positions occupied by representative species, 

 there is found abundant evidence in support 

 of the view also held by Bentham, that the 

 ' interchange between the temperate floras even 

 of the western part of the old world and of 

 the new has mainly taken place via A^ia.' 

 Gray further observes that such considerations 

 ' suggest an ancient continuity of territory be- 

 tween America and Asia, under a latitude, 

 or at any rate with a climate, more meridional 

 than would be effected by a junction through 

 the chains of the Aleutian and the Kurile 

 Islands.' ° Two independent chains of evi- 

 dence are thus found to contribute to the same 

 conclusion, while it is further clear from the 

 pakobotanjeal evidence, that the continental 

 connection thus indicated must have existed 

 until at least the close of the Jurassic, and 

 possibly later. As further justifying the posi- 

 tion held by Professor Ward and also showing 

 that the continental connection was not dis- 

 turbed until after the close of the Jurassic, 



° ' Scientific Papers,' II., p. 135 et seq. 



attention may be directed to the fact ' that the 

 Oregon strata rival those of eastern Siberia 

 in the development of ginkgos; while nearly 

 all the more important species made by Hear 

 from the Siberian beds have similar forms 

 in the Oregon strata,' forms which also have 

 been found to extend into the Lower Creta- 

 ceous of the United States and British Co- 

 lumbia. 



One noteworthy feature of the Jurassic 

 Flora as now presented is the addition of some 

 600 specimens of cycads from Wyoming, to 

 the list previously reported by Ward' and then 

 embracing descriptions of all the Jurassic 

 Cycads from Wyoming known at that time. 



In discussing a number of plants from 

 Alaska, which show very strong evidence in 

 favor of Lower Cretaceous age, but which are 

 held to represent the Jurassic because of the 

 strong representation of Jurassic types of 

 Ginkgo, reference is made to some of the work 

 of the late Sir William Dawson, with respect 

 to which exception is taken to the identifica- 

 tion of Ginkgo lepida Heer, a species which 

 Ward holds must be a Baiera. Some doubt 

 is also thrpwn upon the correct identification 

 oi Ginkgo sihirica Heer, both of these species 

 having been recognized by Dawson in the 

 Kootanie of Canada. Attention is drawn to 

 this opinion at the present time because, as 

 shown by recent studies of the Kootanie flora, 

 Dawson's determinations were correctly made; 

 and although, as stated by Ward, the ginkgos 

 had become nearly extinct on the American 

 continent in Lower Cretaceous times, even in 

 those parts where they had been so prominent 

 in the Lower Oolite, there is not wanting 

 abundant evidence to show that, even though 

 the only ginkgos of the Lower Cretaceous of 

 the northwestern region are to be found solely 

 in the Kootanie of Canada, this formation 

 bears a representation of the genus which 

 shows a very important extension from the 

 Jurassic, abundantly confirming the earlier 

 conclusions of Sir William Dawson. Eecent 

 collections from the eastern slope of the Rocky 

 Mountains as well as from the Crow's Nest 

 Pass, show an extension of the Kootanie flora 



' U. S. Geol. Surv., XX., 1900, Part II., pp. 382- 

 417. 



