CLIMATIC RELATIONS 263 



summer when the daily maxima do not rise as high in the 

 Rio Negro and the Pampa as in Missiones and Paraguay." 

 While summer temperatures are much higher in the 

 plains region than on the eastern coast, in the same lati- 

 tude, mid-winter temperatures are colder, and the winter 

 isotherm of the same latitude bends a little northward in 

 the plains. The precipitation, as would be expected, 

 decreases from the Atlantic westward, but, as in other 

 prairie regions, points in the Chaco-Pampean plains 

 have greater summer seasonal rainfall than points east- 

 ward in the same latitude. In the southern portion of 

 Argentina, the rainfall increases only to the westward. 

 The belt of 8 to 24 inches annual precipitation is a com- 

 paratively narrow one, but includes a large part of the 

 prairie region, extending from about the northern bound- 

 ary of the Republic to and including nearly all of Pata- 

 gonia. A still narrower belt of lowest precipitation 

 (16 inches and under) lies due north and south near the 

 mountains, but reaches the Atlantic coast in the south. 

 In the northern part of this belt, as above stated, a 

 large portion of the precipitation falls in the summer 

 season (Fig. 77). 



278. Isoclimatic lines. With such extremes of^ cli- 

 mate existing in prairie regions, naturally the isothermal 

 and isohyetal lines take peculiar directions. The odd 

 course of the absolute maximum isotherm in the Chaco- 

 Pampean region, already mentioned, is a good example. 

 In the Chernozem, even the lines representing average 

 data take very unusual courses sometimes. For example, 

 the July isotherm of Orenburg passes southward and is 

 the same as that of the eastern Black Sea, or practically 

 subtropical, while the January isotherm of Orenburg 

 passes northward to the Arctic Ocean. In many instances, 



