8 SIR J. W. DAWSON ON TIIR M[-:SOZOIC FLORAS OF 



of time ami iu the region extending along the Rocky Moimtains, from the 49th to the 51st 

 parallel, of no less than six species of Cycads belonging to at least four generic types ; and 

 these types are quite as much Jurassic as Cretaceous in their affinities. Thus we find the 

 Jurassic flora continuing without a break into the Lower Cretaceous, and we shall 

 find that in beds considerably above, we have the beginning of the Dicotyledonous plants 

 of the Tertiary and Modern periods. Thus, in so fur as the flora is concerned, the divid- 

 ing line is in the middle of the Cretaceous ; and we may speak of the flora of the Lower 

 Cretaceovis as Jïirasso-Cretaceous, while that of the Upper members of the series will be 

 Cretaceo-Eocene. Whether the long-enduring and widely-distributed flora, which we have 

 designated by the former name, was strictly contemporary iu all parts of its range, may be 

 doubted, though its whole migrations were in this one definite period. It is not impossi- 

 ble that it may have been introduced first into the Arctic, and that in a time of insular land 

 and eqviable climate, it made its way slowly south. These questions may, however, be 

 better answered in the conclusion of the paper. 



3. Coniferœ. 



Salisburia (Ginkgo) Sibirica, Heer. (Plate IL Fig. 1.) 



Heer. Jura Flora Ost-sibiriens. 18*76, p. 61, PI. VII. 



"Leaf long, petiolate, palmate, frequently lobed, with 8 to 11 lobes, which are oblong 

 and obtuse at their apices. Veins, for the most part 5 to 6, nearly parallel." 



The leaf thus described by Heer, represents a group of iobate leaves, very widely dis- 

 tributed in the Jurassic and Wealden formations, and originally referred to the ferns, though 

 Brongniart, from the first, owing to their hard and coriaceous texture, doubted the correct- 

 ness of this reference. They were at first placed in the genus Ci/dop/eris, and the old 

 C. digUata, Lindley, from the English Oolite is very near to the present species. They 

 were afterwards removed to the doubtful genus. Baiera, and finally have come to be regarded 

 as taxine leaves allied to those of the Ginkgo tree of Japan, a form represented at the present 

 day by only a single species, limited to the Japanese Islands, but which, iu Mesozoic and 

 Tertiary times, possessed several species distributed over the whole of the Northern 

 Hemisphere. 



Collected near Martin Brook by G. M. D. 



Salisburia (Ginkgo) lepida, Heer. (Plate IL Fig. 2.) 



This species, or perhaps only varietal form, is distinguished by Heer, on account of its 

 long and deeply-cleft lobes, attenuated at base and pointed at apex. It is very near to the 

 Baiera gracilis of Bunbury, from the Yorkshire Oolite, and leaves closely allied are des- 

 cribed by Dunker from the Wealden. 



Locality, Martin Brook, and Coal Creek, G. M. D. 



Salisburia (Ginkgo) nana, S. N. (Plate II. Fig. 3.) 



Leaf small, of four narrow lobes, linear obtuse, and arranged in two pairs. Four sub- 

 parallel veins in each lobe. 



This little leaf appears to be distinct from the above species, unless, indeed, it may be 

 a depauperated variety. 



Collected by G. M. D. near Coal Creek. 



