200 Part III. Chapter 2. 
of the Seguoia forests was on the general forest soil-belt between the individual 
Sierra mountain glaciers. The remarkable gap between the northern and 
southern groves is located exactly in the pathway of the vast mer de glace 
of the San Joaquin and King’s River basins. The other great gap in the belt, 
forty miles wide, extending between the Calaveras and Tuolumne groves, occurs 
exactly in the pathway of the great mer de glace of the Tuolumne and Stanis- 
laus basins, and that the smaller gap between the Merced and Mariposa groves 
occur in the pathway of the Merced glacier. We are, therefore, forced to 
conclude that the Seguosa trees which were widespread in Miocene times were 
restricted by the action of the glacial ice to the California side of the continent 
and that the remnant of a once continuous forest was still further separated into 
isolated groves by the action of local glaciers, such as filled the basins of the 
San Joaquin, Tuolumne and Merced rivers. The action of the glaciers on the 
distribution of other forest trees, illustrated by this clear cut example, must 
have been similar and we have as a result the separation of the original 
forest of North America into the Atlantic and Pacific types. A com- 
parison of the coniferous vegetation of the Rocky Mountains, of eastern North 
America and of the Pacific coast is to be found afterwards (Chapter IV), A 
| 
similar difference shows itself in a comparison of the broad-leaved vegetation & 
of eastern and western North America. When during the glacial period, the 
greater part of North America was covered with ice and later submerged in 
its central plain region beneath the sea, it is not strange that the peculiarities 
of the western and eastern floras manifested, as far back, as Cretaceous times 
should be further accentuated. Many characteristic genera of the Atlantic slopes 
of North America are missing in California, and the prairie region, viz., Asimina, 
Zanthoxylon, Stuartia, Gordonia, Tilia, Robinia, Gleditschia, Gymnocladus, 
Cladrastis, Nyssa, Liquidambar, Viburnum, Clethra, Ilex, Catalpa, Diospyros, 
assafras, Bengoin, Carya (Hicoria), Morus, Ulmus, Fagus, Castanea, Carpinus, 
‚Betula, Magnolia, Liriodendron. There are lacking also many trees which from 
the Tertiary period to the present maintained themselves in North America. 
Common and related species of the following genera occur in eastern and 
western North America: Aesculus, Acer, Rhamnus, Ceanothus, Ptelea, Euonymus, 
Acer, Negundo, Staphylea, Rhus, Sophora, Cercis, Prunus, Pirus, Crataegus, 
Amelanchier, Calycanthus, Philadelphus, Ribes, Cornus, Sambucus, Viburnum, 
Symphoricarpos, Lonicera, Cephalanthus, Gaultheria, Kalmia, Styrax, Fraxinus, 
Platanus. On the other hand, the plants mentioned below are peculiar to 
western America: Fremontia californica, Larrea mexicana, Cneoridium dumosum, 
Zizyphus Parryi, Karwinskia Humboldtiana, Adolphia californica, Glossopetalon 
nevadense, Prosopis, Parkinsonia with two species, Canotia holacantha, Char- 
pentiera calıfornica, Whipplea modesta, Menodora with many species. That this 
separation took place during and subsequent to the glacial period is proved 
by the discovery in the Pliocene deposits of California of remains of Platanus 
occidentalis and species of Magnolia. LESQUEREUX ') has discovered at Golden 
1) LESQUEREUX in Hayden Report 1872: 371-427. 
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