Vegetation south of the Land Ice. 197 
Pentstemon Roezli Regel. Castilleia affınis H. & A. 
» Newberryi A. Gray. > miniata Dougl. 
Mimulus implexus Greene. Orthocarpus pilosus Wats. 
» primuloides Benth. Pedicularis attollens Gray. 
Eu. — Veronica alpina L. — » semibarbata Gray. 
» Cusickii A. Gray. Monardella odoratissima Benth. 
5. The Vegetation Zones south of the Land Ice. 
Down off the mountains during the glacial period existed glacial plants which 
formed bog and dryland associations, as previously mentioned. These with 
numerous sedges and grasses formed the tundra vegetation which skirted 
the southern edge of the great continental ice field. During the maximum 
glaciation, many plants were distributed only in the eastern part of North 
America. The following widely spread arctic-alpine species occupied Green- 
land, Labrador and the White Mountains and did not occur in the Rocky 
Mountains. Thalictrum alpinum, Arabis alpina, Arabis stricta, Draba frigida 
(= D. tomentosa), Lychnis alpina, Alsıine stricta (= Arenaria lapponica), 
Arenaria ciliata, Cerastium trigynum, Potentilla alpestris (= P. aurea), 
Alchemilla alpina, Epilobium origanifolium, Saxifraga aizoon, S. adscendens, 
Bupleurum ranunculoides, Gnaphalium supinum, Aronicum Clusii (= Doronicum 
hirsutum), Hieracium alpinum, Hieracıum prenanthoides, Gentiana nivalıs, 
Veronica saxatilis (= V. fruticulosa), Bartsia alpina, Pedicularis sudetica, 
Salix phylicifolia, S. arbuscula’). 
South of this existed in all probability a coniferous forest and immediately 
south of the conifers without any sharp demarcation a forest of broad-leaved 
trees. It would appear, then, that the glaciers did not effect the true distribution 
at any great distance from the ice front. The conifers probably came to 
occupy the outer rim of tree vegetation during the glacial period on account 
of edaphic factors suitable to their rapid spread. As we may learn from their 
present distribution, a youthful topography in which erosion is active, a high 
elevation and porous soil, all of which imply great variations in temperature 
and relative humidity, are more favorable to conifers than to broad-leaved 
deciduous trees. 
The mixed forest to which we have referred, as occurring south of the 
arctic tundra vegetation, was a remnant of the great tertiary forest. This 
forest persisted during the period of refrigeration with its greatest denseness 
in the region drained by the Tennessee River and its tributaries. One tongue 
of this forest of less denseness probably reached in a northeastern direction, 
as far north, as a line following the windings of the west branch of the Sus- 
quehanna River to the Blue Ridge, thence along the Blue Ridge to the Schuyl- 
kill River, thence across to the southeast side of the Great Valley and following 
the hills on the south side of the Great Valley to the Delaware River. 
1) EnGLer, A.: Versuch einer Entwicklungsgeschichte der Pflanzenwelt, 1. Teil; 148. 1879. 
