191 
belts, determined by the climatic conditions; but these zones be- 
came narrower the farther southward they were removed. The 
ice edge in New Jersey and elsewhere, consequently, was bordered 
by a belt of plants and animals, such as now occur on the tundras 
or barren grounds of the north. The plants included prostrate 
willows, Lapland Rhododendron, Diapensia lapponica, and sedges. 
Fic. 17. Face of Brother John’s Glacier. (Photo No. 230,786 by Donald 
B. MacMillan. Courtesy of American Museum of Natural History. 
Among higher animals there were reindeer and musk ox, of which 
t 
ica and to Greenland. 
During the period of glaciation, also, variation and the struggle 
for existence continued, the latter with exceptional intensity, in 
the narrow, crowded, and shifting belts, resulting in the survival 
of only the most adaptable forms. Thus new species arose—the 
more or less modified descendants of the forms that started to mi- 
erate southward with the advance of the ice. This gave rise to 
a flora and fauna containing new elements. 
— 
ie last mentioned is now entirely confined to arctic North Amer- 
