A CURIOUS EXPERIENCE 337 



as regards three of the animals, inasmuch as 

 this change was ultimately conditioned by the 

 movements of the fourth, the musk-ox. But 

 we know nothing of the cause which produced 

 the musk-ox migration, which migration re- 

 sulted in such unsettling of life conditions for 

 the wolves, caribous, and foxes of this one 

 locality. Neither can we with our present 

 knowledge explain the causes which in Maine 

 and New Brunswick during the last thirty or 

 forty years have brought about a diminution 

 of the caribou, although there has been an in- 

 crease in the number of moose and deer; wolves 

 cannot have produced this change, for they kill 

 the deer easier than the caribou. Field natural- 

 ists have in such questions an ample opportunity 

 for work of the utmost interest. Doubtless 

 they can in the future give us complete or par- 

 tial explanations of many of these problems 

 which are at present insoluble. In any event 

 these continuous shiftings of faunas at the 

 present day enable us to form some idea of the 

 changes which must have occurred on in- 

 numerable occasions during man's history on 

 this planet. Beyond question many of the 

 faunas which seem to us contemporary when 

 their remains are found associated with those 

 of prehistoric man were really successive and 



