Baseleveling and Organic Evolution. — Woodworth. 231 
vatecl so as to stand at various hights, many of them mountain- 
ous. On the Pacific coast, the correlated coastal shelf was 
built into the Coast Range; on the east coast, the continental 
shelf has been slightly uplifted in the south and somewhat 
depressed in the north. 
The Flora of the Mesozoic underwent alteration. 
The change in the animal life of the Mesozoic was equalled 
by the alteration and advance in the character of the flora. 
The flattening down of the peneplain was attended by tin- 
incoming of the higher vegetable types. "Even with the Ju- 
rassic epoch, the next in succession to the Trias," says Sir 
J. William Dawson,* "there are clear indications of the pres- 
ence of the endogens, in species allied to the screw-pines and 
grasses; and the palms appear a little later, while a few exog- 
enous trees have left their remains in the Lower Cretaceous, 
and in the Middle and Upper Cretaceous these higher plants 
• •a me in abundantly and in generic forms still extant, so that 
the dawn of the modern flora belongs to the Middle and 
Upper Cretaceous." 
Mr. Alfred Russel Wallacef follows Ball's hint as to the 
cause of the late appearance of exogens. The suddenness of 
their appearance, he notes, must be only apparent, being "due 
to unknown conditions which have prevented their preserva- 
tion (or their discovery) in earlier formations." Mr. Ball}; 
has supposed that the monocotyledons and the ferns, equise- 
tums, cycads, and conifers inhabited the lowlands, while the 
dicotyledons grew in the uplands, where there were less pres- 
sure, heat, moisture and CO„ in the air; and on this Mr. 
Wallace remarks that, in the Rocky mountains ferns and 
monocotyledons are scarce in comparison with dicotyledons, 
dryness and rarity of the atmosphere being the cause. Ele- 
vated plateaus and mountains, he states, are more favorable 
to dicotyledons than to monocotyledons, and we may well sup- 
pose that the former originated within such elevated areas 
and were for long ages confined to them. 
If we suppose that the earlier Mesozoic uplands were the 
*Geological History of Plants, pp. 177, L78. 
I Darwinism. Humboldl Library ed., p. '.'in. 
|On the Origin of the Flora of the European Alps, Proc. I!"\ Geog. 
Soc, v«»l. i. 1ST!), pp. 564-588 
