Ixxiv. PRESIDENT'S ADDRESS. 



is first seen in the floras of the Upper Cretaceous strata, showing a 

 dependence upon geographical position that is still more clearly 

 seen in the Miocene Period. In the more recent plant-bearing 

 strata there are not a few instances where plants characteristic of 

 different latitudes are preserved in the same rock. Such a 

 commingling, Mr. Starkie Gardner thinks, is due to repeated 

 cyclical changes in temperature and the resulting migration of 

 plants to warmer or colder climates. In the case of the Eocene 

 plant-beds of Hampshire, Mr. Series Wood suggests that the river 

 whose delta-deposits contain the plant-remains flowed through a 

 district where a tropical climate prevailed on the low-ground and 

 was fed by tributaries which flowed from a mountain region, thus 

 accounting for a mixture of tropical northern forms in delta 

 sediments. Although the evidence afforded by fossil plants in the 

 earlier geological periods is generally considered to point to 

 temperatures in past eras higher than those of the same latitudes 

 to-day, among the Pliocene and post-Pliocene floras, Palseobotany 

 supplies us with facts suggestive, in some cases, of colder condi- 

 tions than those of the present day. Among the Tertiary floras of 

 Australia and New Zealand there is a large number of plant-types 

 congregated together such as now characterise widely separated 

 latitudes, which is difficult to understand from the point of view 

 of climate or other physical conditions of environment, but it may 

 be explained by regarding it as a composite type of flcra not yet 

 differentiated into its various branches. 



RUSHMORE. 



The further the examination of the Rushmore earthworks and 

 ditches is proceeded with, the more they confirm General Pitt 

 Rivers's theory that their age can, within certain limits, be ascer- 

 tained by a risid attention to the character and position of the 

 pottery, as accurately as the comparative age of a series of 

 geological beds the oldest invariably underlying the newer. 

 In like manner the earliest pottery of an earthwork invariably lies 

 at the bottom of the ditch, and if, during the process of silting up, 



