FIG. 21-4 The largest black area shows the present main range 

 of the eastern tour-toed salannander. The smaller spots in the 

 southern states represent boreal relicts of a wide southern dis- 

 tribution during the height of the glacial advance. The isolated 

 group in Nova Scotia may also represent a relict from a more 

 northern dispersal of the species during the post-glacial climatic 

 optimum (Smith 1957). 



Deevey (1949) and Dorf (1960), the climate every- 

 where south of the glacial front was considerably re- 

 frigerated, deciduous forest was driven into refugia 

 in Florida and Mexico, and tundra and coniferous 

 forest prevailed everywhere in between. Griscom 

 (1950) believes that continental refrigeration ex- 

 tended well into Mexico, causing extensive south- 

 ward dispersal of northern birds and the elimination 

 of the South American element previously present. 

 Speciation supposedly occurred in populations of 

 certain birds (Huntington 1952) and amphibians, 

 reptiles, and mammals (Blair 1958) that became 

 fragmented and isolated from each other in the 

 Southeastern and Southwestern refugia. There is a 

 likelihood, however, that these animals were segre- 

 gated into southeastern and southwestern popula- 

 tions, not by effects of cold climate, but by the 

 southward extension of grassland to the Gulf. It is 

 probable that, during the Pleistocene period, there was 

 either grassland or a tenuous savanna type of habitat 

 in Texas that separated the forests of Mexico and 

 those of the southeastern states ( Martin and Harrell 

 1957). The broad cold waters of the Mississippi 

 River may also have split and isolated eastern and 

 western populations of some animal species at the 

 times when melting of the glaciers was at its height. 

 In Europe and Asia, westerly winds were di- 

 verted south into the Mediterranean region, and high 

 anticyclonic barometric pressures developing over 



the glacier brought dry, cold, northeasterly and east- 

 erly winds. Loess was deposited in a broad belt from 

 western France east into the Balkans and northeast 

 into Russia (Zeuner 1945). True tundra graded into 

 loess and bush tundra and coniferous and deciduous 

 forests are thought to have been forced into refugia 

 in Spain, Italy, and the Balkans ; there is some doubt, 

 however, that the forests were displaced so far south 

 (Hare 1953). The Mediterranean climate was, how- 

 ever, probably cooler and moister during the height 

 of glaciation than it is at the present time (Zeuner 

 1945). 



POST-PLEISTOCENE 



Retreat of the glacier 



The melting of the ice was quite rapid, per- 

 haps 134 m (440 ft) per year in the Great Lakes 

 region (Flint 1957). Meh water filled depressions 

 to form vast pro-glacial lakes. Sea-level rose 1 m 

 (3.5 ft) per century between 18,000 and 5000 B.C., 

 but the sea apparently has risen very little since then 

 (Russell 1957). The Great Lakes, in their early 

 stages, had outlets down the Hudson and Mississippi 

 Rivers and had different interconnections than at 

 present. Still later. Lakes Agassiz, Ojibway-Barlow, 

 and others were formed in the north. A knowledge 

 of these lakes and the history of past drainage sys- 

 tems is prerequisite to interpretations of present-day 

 distributions of aquatic organisms. 



With the melting back of the ice, local glaciers 

 were left in the Catskill Mountains of New York, on 

 Mount Katahdin in Maine, in the Shickshock Moun- 

 tains on the Gaspe Peninsula, in Newfoundland, and 

 in Labrador. The glacier receded faster in the west- 

 ern interior of Canada between the Rocky Mountains 

 and Hudson Bay than it did to the East. There is 

 evidence that the glacier disappeared from the 

 Hudson Bay region while still persisting over the 

 highlands of Quebec and the Labrador Mountains. 

 The last of the glacier still remains on the mountains 

 and plateaus of Baffin, Devon, EUesmere, and Axel 

 Heiberg Islands, and in Greenland (Flint 1947). 



Identification of kinds of pollen and comparative 

 counts of pollen grains from various depths in peat 

 bogs gives us a picture of the predominant vegeta- 

 tion, and consequently the climate, in the vicinity of 

 the bogs at various times in the past (Sears 1942, 

 Deevey 1949). A chronology is given for North 

 America and Europe in Table 21-1. The time scale is 

 determined, in part, by measuring the radioactivity of 

 carbon. C', obtained from samples taken at various 

 depths in glacial deposits. Radioactive carbon disin- 

 tegrates in non-living matter at a progressive rate; 



288 Geographic distribution of communities 



