MAMMALS OF PENNSYLVANIA AND NEW JERSEY. 3 



faunae or life-zones of Pennsylvania and New Jersey, I will quote G. S. Miller, 

 Jr.'s, lucid remarks thereon, given in his "Preliminary List of the Mammals 

 of New York," " The importance of an acquaintance with the life-areas of 

 a region, as a key to the geographic distribution of the animals and plants, is 

 hardly to be over-estimated. Such knowledge furnishes ready and exact 

 means of defining the ranges of species without the tedious enumeration 

 of isolated localities, and offers moreover an explanation of the principal 

 factor governing those associations of species that constitute local faunae 

 and florae. Briefly defined, a life-zone is a trans-continental area bounded 

 Ijy certain isothermal (average temperature) lines, and characterized by 

 relative uniformity of fauna and flora. Together with the isotherms a life- 

 2one normally extends in an approximately east and west direction, but both 

 are subject to endless deviations. Elevations in the surface of the earth 

 cause the life-zones to bend to the southward, often many hundreds of miles 

 beyond their sea level position. Furthermore, a life-zone is not necessarily 

 continuous. It often happens that isolated hills or mountains reach a suffi- 

 cient height to have about their summits the climatic conditions char- 

 acteristic of a more northerly zone than at their bases. Effects similar to 

 those of elevation are produced by isolated swamps and cold rock slides." 



Illustrative of these remarks we find on looking at the map of Pennsylvania 

 that the higher Alleghanian chain bearing the Canadian fauna on its crest, 

 •cuts the eastern and western extension of the transition zone in half, while 

 the valley of the upper eastern branch of the Susquehanna brings about a 

 reversal of these conditions by bisecting the Canadian zone with an offset of 

 the Transition. In Fayette and Somerset Counties a most striking alterna- 

 tion of Austral, Canadian and Transition zones occurs as we travel along the 

 Maryland line, due to the intrusive parallel range of the Alleghany ridge. 

 Laurel ridge, and Chestnut ridge, with their intervening valleys. In the 

 tipper Austral zone of south New Jersey the " boreal " or transition islands of 

 cool, dense-shaded cedar swamp and bog are a striking illustration of local 

 conditions, and a like instance is the typical Canadian fauna of certain 

 tamarack and fir swamps set in the midst of otherwise doubtfully Canadian 

 regions in the northern part of both states. 



In North America seven life zones are represented. These are (begin- 

 ning at the north) the Arctic, Hudsonian, Canadian, Transition, Upper 

 Austral, Lower Austral and Tropical. The temperatures limiting three life 

 areas formed in our limits are tabulated as follows, by Merriam : — These are 

 based on the two laws "(i) The northward distrihuiioti of animals and 

 plants is determined by the total quantity of heat— the sum of the effective tem- 

 peratures. (2) The southward distribution of Boreal, Transition zone and 

 Upper Austral species is determined by the 7nean temperature of the hottest 

 part of the year y Southern limit of the Canadian zone is defined by the iso- 



