THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



Akt. XX Y. — The effect of Giaciation and of the Glacial 

 Period; on the present Fauna of North America / by 

 Samuel H. Sc udder. 



The time has perhaps arrived when at least a beginning- 

 may be made in an investigation which shall show with some 

 degree of exactitude just what amount of influence the Glacial 

 Period has exerted upon the present distribution of animal 

 life in North America. Within a few years, and with a degree 

 of precision sufficient for our purpose, geologists have mapped 

 the areas which were once completely buried beneath the 

 northern ice-sheet, and which were then absolutely devoid of 

 animal life. "With the slow southward advance of the ice, 

 animals were crowded southward ; with its recession they 

 advanced again northward to reoccupy the desolated region, 

 until now it has long been repopulated, either with the direct 

 descendants of its former inhabitants or with such limitations 

 to the integrity of the fauna as this interruption of local life 

 may have caused. Precisely what modifications may have 

 resulted, what probable resemblance the present fauna bears to 

 that which preceded it before the interruption of its occu- 

 pancy of the whole area, is the problem before us, though we 

 shall only attempt a first step toward its solution. 



In considering this question it occurred to me that some 

 light might be thrown upon the matter if one were to tabulate 

 separately the animals of the. eastern half of the continent 

 now found (1) upon the area once covered by the ice-sheet and 

 (2) upon the driftless area, using the mapped limits of the 

 terminal moraine to separate the two regions ; to discover how 



Aji. Joub. Sci.— Third Series, Vol. XLVIII, No. 285.— Sept., 1894. 

 12 



