358 E. C. ANDREWS. 
Glacial Period connotes either rapid modification, or migra- 
tion, of tertiary plant types respectively within, or from, 
any given district affected. 
The Age of Dicotyledons, 
With notes on generic determinations of Angiosperms on 
the evidence of leaves alone. 
In any discussion as to the age of a particular family or 
order of the Dicotyledons, it would be necessary in the 
first place to ascertain the morphological position occupied 
by such family, or order, in its subclass; and, in the second 
place, to ascertain if possible, the geological age of the 
subclass or class itself. 
With regard to the first point, it would appear that the 
Leguminosze are types which are highly developed, as 
compared with many families of the Dicotyledons, such as 
the Casuarinez, the Juglandacee, the Salicinez, the Cupu- 
liferze, the Ulmacez, and the Moracez. This suggests 
that the present families of the Leguminosze had not been 
outlined until the earlier forms of the dicotyledons had 
been well established and differentiated. 
With regard to the second point, it may be mentioned 
that no undoubted plant remains of dicotyledonous nature 
have been found in beds older than the lower Cretaceous. 
On the other hand they have been recorded from the oldest, 
of these beds in the Atlantic Coast area of the United 
States, while from the younger beds of the Lower Creta- 
ceous, Dicotyledons have been recorded throughout North 
America." 
‘*In Portugal primitive types of Angiosperms appear in 
the Lower Cretaceous, but apparently not so low down in 
the series as the Potomac of North America. . . . The 
view that seems best justified at the present stage of 
1 Chamberlain and Salisbury (24) pp. 130-138. 
