562 THE FRESH-WATER LOCHS OF SCOTLAND 
European settlers. Another,^ recently advanced, is that the rivers 
which have their origin in the humid, wooded tops of the higher 
areas erode away the margins of the rain-collecting highlands in their 
descent towards lower and more arid levels, and gradually diminish as 
they destroy their rain-collecting areas. 
The chief lakes of the basin in the Durango district are : — 
Laguna de Tlahualila, which receives no streams of any size ; Laguna 
del Muerto or Mayran, which receives the waters of the River Nazas ; 
and Laguna Parras, into which flows the Aguanaval. These all lie 
comparatively close together, and none of them has an outlet. The 
fact that there exist in the River Nazas species of fish which occur 
also in the Rio Grande is further proof of the former existence of 
a connection between these inland basins and the Rio Grande. 
The same conditions continue northward into Chihuahua, New 
Mexico, and Western Texas, which receive the drainage of the plateau 
of the Sierra Madre. The lakes in this area are comparatively small. 
The two principal ones are Laguna de Guzman, into which flows 
the River San Miguel, and Laguna de Santa Maria, into which drains 
the river of the same name. 
In Central America lakes without outlet are common in the 
limestone region of Northern Guatemala, the largest being Lake 
Peten, and in the rainy season many shallow temporary lakes 
{akalches) are formed in the hollows of the same region. Numerous 
lagoons of brackish water lie along both coasts. 
This concludes our survey of the lakes situated in the inland 
drainage areas or desert regions of the Northern Hemisphere. When 
Southern we turn to the similar areas of the Southern Hemisphere we find that. 
Hemisphere. ]3gcause of the less developed land-masses, these areas are — excepting 
Australia — very limited in extent when compared with their northern 
analogues. 
Australia. Australia may be described as a plateau fringed by well-watered 
coasts, with a depressed, and for the most part arid, interior. Nearly 
two-thirds of the inland drainage area of Australia, which is estimated 
by Murray at 1,556,000 square miles (see fig. 67), is occupied by the 
Great Austral Plain, flanked on every side by mountains and table- 
lands, and sloping more or less gradually to a central depressed lake 
region. The plain is subdivided by undulating downs, or flat-topped 
hills, with here and there some scattered mountain groups. Where 
the rainfall is not all absorbed by the soil or lost through evaporation, 
the depressions are occupied by saline ^ lakes. 
^ R. T. Hill, " Characteristics of some Mexican Mining Regions," Engineering 
and Mining Journal (New York), vol. Ixxxiv. p. 633, 1907. 
2 See second footnote on p. 515. 
