FAUNA OF AMERICA — CLARK 291 



level and diversified highlands up to 14,000 feet in Guatemala. Arid 

 regions with cactus grade into dense tropical forests, and these into 

 pine forests. The islands also are greatly diversified. Some, like the 

 Bahamas, Antigua, and Barbados, are low and flat, chiefly of coral 

 formation, but most of the others consist largely or mainly of heavily 

 forested mountains rising to 9,000 feet in Haiti and more than 7,000 

 feet in Jamaica. 



Most of South America is low. The great chain of the Andes, with an 

 average height of 11,000 to 12,000 feet, runs close to the western border 

 with an eastward spur along the Caribbean coast. The Guiana high- 

 lands separate most of the Orinoco Valley from that of the Amazon, 

 and in eastern Brazil are the extensive Brazilian highlands. The 

 lowlands vary from dry and partly barren through areas covered with 

 rank herbage, permanently or seasonally, to the dense forests of the 

 Amazon Valley, especially the western half. These forests are unique 

 in being canopy forests consisting of vast masses of vegetation tied 

 together with vines and supported by tree trunks, with sparse under- 

 growth, in many areas flooded during the rainy season. 



FAUNA OF NORTH AMERICA 



In the treeless high Arctic zone, the southern limits of which are 

 sometimes north and sometimes south of the Arctic Circle, the animals 

 of North America are almost wholly circumpolar, as the caribou (rein- 

 deer), polar bear, Arctic wolf, fox, hare, lemmings, and weasels. 

 Most characteristic of the mammals of the American Arctic is the 

 musk ox, now extinct in the Old World, living in the far north from 

 east of the Mackenzie Eiver to northern Greenland. Of the 65 genera 

 of birds 60 are circumpolar, including the ptarmigan, gyrf alcon, snowy 

 owl, snow bunting, and many others. Fresh-water fishes are few — 

 only some trout ; the three-spined stickleback ; and the Alaska black- 

 fish {Dallia) of Alaska and Siberia, which is frozen in the ice for a 

 considerable part of each year. There are no reptiles or amphibians. 

 The insects are mostly circumpolar, and as in all regions where con- 

 ditions are unfavorable for animal life, the Diptera, or two-winged 

 flies, predominate. Biting flies, especially mosquitoes and black flies 

 {Simulium) , are especially abundant. The butterflies are all familiar 

 Old World types. 



Farther south in the region of the forests there is a marked increase 

 in animal life. Distinctively American types now appear, there is a 

 considerable difference between east and west, and in the western 

 mountains there is a continuation into America of Old World mountain 

 or alpine forms. Old World animals of general distribution are repre- 

 sented by the moose, caribou, wolf, foxes, bears, lynxes, wolverines, 

 martens, weasels, otters, the varying hare, squirrels, and other rodents, 



