1914 ] 
Jackson: Land Vertebrates of Ridgeway Bog 
41 
is probably of northern origin, and Microtus pennsylvanicus may 
be also. The majority of the species found in these two associa- 
tions, nevertheless, have southern affinities. Many of these forms 
undoubtedly existed at the edge of the glacier or even on the 
covering of debris on the glacier itself, or in oases in the ice sheet; 
others, many of which may have been driven south by the ice 
sheet, followed at intervals the recession of the ice. 
The biota of the Cassandra-Tamarack-Spruce Associations of 
Ridgeway Bog is typical of northern North American bogs; it 
consists of such characteristic forms as Larix laricina, Picea 
mariana, Alnus incana, Sarracenia purpurea, Spiraea salicifolia, 
Potentilla palustris, Kalmia glauca, Ledum groenlandicum, Cha- 
maedaphne calyculata, Steironema quadriflorum, Oxycoccus oxy- 
coccus, Canachites c. canace, Nuttallornis borealis, Nannus hiemalis, 
Sitta canadensis, Regulus satrapa, Hylocichla g. pallasii, Sorex 
personatus, Sorex richardsonii, Neosorex palustris, and a few other 
associated species. 
It is this biota which some have led themselves to believe was 
driven south considerable distance beyond the edge of the ice 
sheet (fig. 9) during the Glacial Epoch and which has since remi- 
grated north into the glaciated area. The evidence upon which 
such an assumption can be based is, to say the least, unsatisfac- 
tory and meager, and the proof lies upon him who upholds such 
an hypothesis. The entire evidence at present is based upon the 
occurrence towards the south of a very few Pleistocene fossils of 
animals having present-day arctic affinities. Adams writes: 
“For example, the occurrence in Pleistocene times (Hay, '02; 
Hatcher, ^02) of such arctic types as the walrus in Virginia and 
South Carolina along the Atlantic coast, the musk ox in Pennsyl- 
vania, West Virginia, Kentucky, Indian Territory and Iowa, 
and the reindeer in New Jersey, Pennsylvania, Kentucky and 
Iowa, certainly shows that an arctic climate once reached far to 
the south. Although limited, this information clearly suggests 
the general extreme southern limit reached by arctic types during 
the Ice Age’’ (Adams, 1905, p. 55). 
On the strength of these few fossils it seems to me hardly logical 
to conclude that an arctic climate prevailed at one time in the 
regions designated. It must be remembered that none of these 
animals is conspecific with an existing arctic form, and that in 
