4 SIE J. W. DAWSON ON THE MESOZOIO FLOE AS OF 



that of the Laramie, which at present is held by Cope and others, on the evidence of its 

 animal fossils, to be Cretaceous, while by Lesquereux its flora is regarded as Eocene. On this 

 question I may remark that as far back as 18Y5, (when my attention was first called to the 

 flora of this group, by the collections made by Dr. G. M. Dawson in his explorations on the 

 49th parallel,) I held, on the evidence of the plants, though contrary to what I then be- 

 lieved and still believe to be inaccurate conclusions of certain European palœobotanists, that 

 it should be regarded as a transition group connecting the Cretaceous and the Eocene, and 

 at the same time I stated reasons for believing that the so-called Miocene of Mackenzie 

 Eiver, and of the Fort Union group in the United States, was probably of the same age. 

 I have since that time seen no reason to change my opinion, but on the contrary have 

 found evidence to show that the Laramie flora, or several of its species, may be traced 

 downward into the Cretaceous as far as the beds known as the Pierre group of the geolo- 

 gists of the United States, and those called the Belly Eiver group by the officers of the 

 G-eological Survey of Canada. I have been pleased to observe that in Yol. VIII of the 

 Eeports of the U. S. -Greological Survey of the Territories (1883), Lesquereux now admits 

 that the Laramie is Lower Eocene; and I have no doubt that, as the evidence accumulates, 

 he will come over to the opinion that its flora is really that of the newest Cretaceous ; as 

 it has long been held to be in the Canadian territory. It is to be observed, however, that 

 this will carry with it important modifications of opinion as to the Cretaceous and Tertiary 

 floras of the whole northern hemisphere, — points to which I am glad to see that Mr. Starkie 

 Gardner has recently called attention in Great Britain, and to which I shall refer in the 

 sequel of this paper. 



I shall now proceed to describe the new plants which have been obtained from the 

 Kootauie and Mill Creek series and the intermediate beds, and to discuss their relations 

 to those elsewhere known in the Mesozoic and Tertiary. "With reference to the generic 

 names assigned to these plants, I would desire it to be understood that they are intended 

 to indicate, in the case of leaves more especially, their resemblance to modern genera, but 

 without any dogmatic assertion as to precise affinities. Many dicotyledonous leaves of the 

 Cretaceous might be referred with almost equal probability to several modern genera, and 

 since we know that, in modern times, certain genera present in their different species modi- 

 fications of foliage more or less imitative of those of other groups, we may well hesitate in 

 affirming that a particular type of leaf was, in Cretaceous times, associated with precisely 

 the same kind of fructification as that which accompanies it in modern times. At the same 

 time it is well known that many kinds of foliage, especially in the case of trees, are mark- 

 edly characteristic of particular groups ; and, since we cannot fairly conclude that the 

 connection of a certain type of leaf with a certain structure of stem and character of fruit 

 is an accident, but must believe that it depends on some law of physiological correlation, 

 we have good reason to rely on this when other evidence is absent. I may state, however, 

 as the result of my experience in many cases, that the conclusions deduced from the leaves 

 haA'e often been confirmed, by the subsequent discovery in association with them of the 

 tissues of their stems, and of the forms of their fruits. It is also to be observed that, 

 plants afford indications of climate and other physical conditions, even more trustworthy 

 than those which can be obtained from animal fossils. From a geological point of view 

 it is to be observed, that while the names assigned to particular leaves may be dis- 

 putable, the occurrence of the leaves themselves in certain strata over wide areas affords 



