644 RELATION TO ENVIRONMENT. 



along the Pacific coast permits northern species to come far south, while 

 the high sum total enables southern species to push northward as far 

 as Puget Sound. Such an extensive overlapping of Boreal and Austral 

 faunas does not occur elsewhere in North Amerca, and for the evident reason 

 that no area approaching it in extent has so equable a temperature. 



"In most parts of the United States it is easy to distinguish the bound- 

 aries between the Transition and Upper Austral zones, but in the Pacific 

 Transition area these distinctions are nearly obliterated, a large portion 

 of the species ranging in common over both belts." 



The Upper Austral Zone. "The Upper Austral zone may be divided 

 into two large and important faunal areas an eastern humid or Carolinian 

 area and a western arid or Upper Sonoran area, which pass insensibly 

 into one another in the neighborhood of the one-hundredth meridian." 



a. The Carolinian Area. "The Carolinian area occupies the larger 

 part of the Middle States, except the mountains, covering southeastern 

 South Dakota, eastern Nebraska, Kansas, and part of Oklahoma; nearly 

 the whole of Iowa, Missouri, Illinois, Indiana, Ohio, Maryland, and Dela- 

 ware; more than half of West Virginia, Kentucky, Tennessee, and New 

 Jersey, and large areas in Alabama, Georgia, the Carolinas, Virginia, 

 Pennsylvania, New York, Michigan, and southern Ontario. On the 

 Atlantic coast it reaches from near the mouth of Chesapeake Bay to south- 

 ern Connecticut, and sends narrow arms up the valleys of the Connecticut 

 and Hudson rivers. A little farther west another slender arm is sent 

 northward, following the east shore of Lake Michigan nearly or quite to 

 Grand Traverse Bay. These arms, like nearly all narrow northern pro- 

 longations of southern zones, do not carry the complete faunas of the 

 areas to which they belong, but lack certain species from the start 

 and become more and more dilute to the northward until it is hard to say 

 where they really end. Their northward boundaries, therefore, must be 

 drawn arbitrarily or must be based on the presence of particular species 

 rather than the usual associations of species. 



"Counting from the north, the Carolinian area is that in which the 

 sassafras, tulip-tree, hackberry, sycamore, sweet gum, rose-magnolia, red- 

 bud, persimmon, and short-leaved pine first make their appearance. 

 Chestnuts, hickory-nuts, hazelnuts, and walnuts grow wild in abundance. 

 The area is of very great agricultural importance. 



" Cereals do well in the Carolinian area, particularly wheat and corn. 

 The sugar-beet is an important crop in the northern parts, but fails to 

 develop sufficient sugar for profitable culture in the southern parts." 



b. The Upper Sonoran Area. "It covers most of the great plains in 

 eastern Montana and Wyoming, southwestern South Dakota, western 

 Nebraska, Kansas, Oklahoma and Texas, and eastern Colorado and 

 New Mexico. . In Oregon and Washington it covers the plains of the 



