SILVER FOX FARMING. 
and plant life have a certain uniformity. To determine the regions 
suitable for fox farming, therefore, it is necessary to learn the areas 
within which foxes are known to produce superior fur. Records of 
«2 '3 
the Biological Survey show that such localities occur only north of 
the southern boundary of the Canadian Zone. This boundary, as 
shown on the accompanying map (fig. 2), crosses the States of Maine, 
New Hampshire, Vermont, Michigan, Wisconsin, Minnesota, and 
