764 ROLLIN T. CHAMBERLIN 
Pampa Aullagas, are well enough known, but in addition there 
are many minor lake flats, dry or nearly so, which escape notice. 
It is on some of these old lake bottoms that the great borate deposits 
of South America occur. But here the geographic distribution 
of the lakes which contain borax is of significance, as it is found 
that the deposits of borax are largely confined to those lakes which 
lie close to the volcanoes of the Western Cordillera. Away from 
the volcanoes, whether eastward over the central plateau, or 
westward down the long desert slopes leading toward the coast 
where the nitrate beds abound, the borates rapidly disappear. 
The borates thus seem to be related to the volcanoes. The nitrates 
occur on open salinas at moderate elevations, 3,000—-5,000 feet, 
and not far back from the coast. ‘The borax fields, on the other 
hand, are located high up on the edge of the tableland close to 
the base of the big volcanoes. Both nitrates and borates are 
dependent for their accumulation and preservation upon the 
extreme aridity of the region, but the sources of the nitrogen and 
the boron are quite different. 
The Salinas of Ascotan may be taken as a typical case to show 
the probable source of the borates. The railroad from Anto- 
fagasta to Bolivia creeps steadily upward from the coast and 
reaches its highest point in crossing the Western Cordillera at the 
station of Ascotan, which is about 13,000 feet above the sea. 
The Western Cordillera here consists of volcanoes most of which 
have only recently become extinct, while, from a few, smoke is 
still escaping. In the neighborhood of Ascotan the cones rise to 
heights of 17,000-19,500 feet. But in spite of the great altitude 
only an occasional patch of snow is seen on these lofty peaks 
owing to the extremely scanty precipitation, for this region lies at 
the northern end of the desert of Atacama. 
After climbing up to Ascotan the railway runs parallel to the 
line of volcanoes and the great borax lake of Ascotan comes into 
view. ‘This lake is perhaps ro miles long and 3 miles wide, extend- 
ing northward parallel to the range to a point beyond Cellobar. 
It fringes the base of a line of volcanoes which begin at the south 
in the cone of San Pedro y Pablo (19,400 feet) and end north of 
the lake in the smoking volcano of Ollagiie (19,200 feet). The 
