CENOZOIC TIME — QUATERNARY. 945 



the higher summits at intervals, even as far south as iSTew Mexico. Again, 

 there were isolated glacier regions along the Cascade Eange and the Sierra 

 Nevada, about Eainier, St. Helens, Hood, Shasta, Lyell, and other summits ; 

 and in the Great Basin, on Jeff Davis Peak, the East Humboldt Range, 

 Shoshone Eange, and West Humboldt Eange. Shrunken relics of the old 

 glaciers still linger about the Wind Eiver Mountains in Wyoming; on 

 Mount Lyell and Mount Dana in the Sierra Nevada ; and on Shasta, Eainier, 

 and other summits of the Pacilic coast region. 



East of the summit range of the Eocky Mountains in British America, 

 the limit between the eastern drift, or that from the region east of Lake 

 Winnipeg, and the western, or that of the mountains beyond, has the posi- 

 tion shown by the dotted line on the map, Fig. 1548, the height being 3000 

 to 3700 feet above sea level. 



There was also a northern limit to glaciation in northwestern America^ 

 according to G. M. Dawson. The line crossed the plateau region of British 

 Columbia, between 60° and 64° N., and consequently Alaska was uncovered 

 — a fact confirmed by the more recent observations of Dall and Eussell. 

 Greenland had probably no more ice than now. 



The details on the map (Fig. 1548) with reference to the moraines from the Mississippi 

 to New Jersey have been obtained chiefly from published and unpublished notes of 

 Chamberlin and Leverett ; those over Iowa and Minnesota, from W. Upham ; those about 

 the Coteau des Prairies, from I. E. Todd ; and those farther north, from G. M. Dawson ; 

 for the position of the southern ice-limit, or Moraine line A, from H. C. Lewis, Report Z ; 

 The Terminal Moraine in Pennsylvania, 1884, from G. F. Wright ; for the line westward 

 to the Mississippi, Lewis's Report Z, and also Wright's Ice Age, etc. ; for the positions 

 of the glacial lakes of Manitoba, from W. Upham ; those of the lakes of the Great Basin, 

 from G. K. Gilbert and I. C. Russell ; for the glacial strise over New England, from 

 C. H. Hitchcock mainly ; and those of other regions from Chamberlin's map, 1th Ann. Bep. 

 U. S. G. 8., and other sources. 



Condition outside of the Ice-limit. Forced migration. — South of the Ice- 

 limit, the precipitation was probably as heavy as to the north of it. But it 

 made only deep snows about the Appalachians and other low mountains, 

 and contributed water abundantly to rivers and lakes. Over a narrow belt 

 near the front, there would have been marshes and ponds with Arctic vege- 

 tation, and cold-climate Mammals, which had been driven southward. 



Several of the emigrant plants still remain and thrive on the summits of 

 the mountains of both eastern and western North America. Thirty-seven 

 species, according to Asa Gray, occur on the White Mountains of New 

 Hampshire, and part of them also on the Adirondacks and Green Mountains. 

 Out of 27 species observed by the Jensen expedition on a Greenland Nunatak 

 in 1878, the White Mountain flora includes, according to Gray, the Grasses 

 Luzula hyperhorea and Trisetum subspicatum, the Sorrel, Oxyria digyna, the 

 Moss-like Heath, Cassiope hypnoides, and the Moss-like Catchfly, Silene 

 acaiclis. Sedum rhodiola, a subalpine species, occurs on cliffs of the Dela- 

 ware, below Easton, Pa. ; Saxifraga oppositifolia Linn., on Mount Willoughby, 

 i> ana's manual — 60 



