4:26 Wt >rtm a n — St udies of Eocene Mammalia in the 



which include two Algae, two Fucoids, one Hepatic, one Chara, 

 three Equiseta, twenty-three Ferns, twenty-one Cycads, twenty- 

 four ( Jon iters, and one Monocotyledon. It is remarkable for 

 the entire absence of Dicotyledons. The lowermost Cretaceous 

 beds of Portugal, which are considered to be equivalent in age 

 to the Wealden, have, according to the same authority, yielded 

 two Algae, two Hepatics, three Lycopods, two Equiseta, 

 8eventy-nine Ferns, fifteen Cycads, twenty-nine Conifers, six- 

 teen Monocotyledons, forty-seven Dicotyledons, five anomalous 

 types classified as Proangiosperms, and three forms of uncer- 

 tain reference. In like manner, the Potomac formation of 

 America contains Ferns, Cycads, Conifers, Monocotyledons, 

 and Dicotyledons, in nearly the same proportion as the beds of 

 Portugal. The character of this flora gives unmistakable 

 evidence of a tropical climate, and while we are not able to 

 say whether the temperature was actually higher than in 

 Greenland during the deposition of the beds supposed to be of 

 the same age, we may feel perfectly certain that tropical con- 

 ditions were wide-spread over the .Northern Hemisphere during 

 the early part of the Cretaceous. 



In the basal strata of the Lower Cretaceous, no remains of 

 true Dicotyledons have as yet been found. Higher up in the 

 series they occur sparingly, but toward the top of the section 

 they suddenly appear in great numbers and variety. Thus, in 

 the Gault of England and in beds of corresponding age in 

 Portugal are found the leaves of Poplar, Magnolia, Myrtle, 

 Willow, Walnut, Maple, Sassafras, Fig, Cinnamon, Holly, Oak, 

 Redwood, and Palms. In America, in beds of approximately, 

 if not identically, the same age, occur Sassafras, Tulip-Tree, 

 Magnolia, Aralia, Cinnamon, Poplar, Willow, Maple, Birch, 

 Chestnut, Alder, Beech, Elm, Sequoias, and Palms, the leaves 

 of some of the latter being ten feet in diameter. The leaves 

 of a few Cycads are present, but they are not so abundant as 

 they were in the lower stages, and here represent a waning 

 group. 



In a survey of this flora as a whole, together with a con- 

 sideration of the manner of occurrence of certain of its 

 constituent elements, two facts of more than ordinary impor- 

 tance force themselves upon the attention of the investigator : 



(1) There is an astonishing similarity or striking resemblance 

 between these Cretaceous plants of .Europe and America ; and 



(2) the higher Angiosperms appear in identically the same 

 manner in these two widely separated areas, by sudden intro- 

 duction as if by impulses or waves of migration. 



In regard to the first of these propositions, Ward in his 

 excellent paper has shown that the early Cretaceous florae of 



