766 ROLLIN T. CHAMBERLIN 
scanty precipitation which falls upon the basin and its volcanic 
borders, and the loss by evaporation. Necessarily there is a con- 
centration of salts as evaporation goes on. All salts dissolved 
by waters which trickled through the volcanic cones and reached 
the lake flat would gradually become concentrated there as the 
water evaporated and would finally be deposited as a solid in- 
crustation. 
The water entering the lake, whether directly or by the under- 
ground route, can have come in contact with little besides volcanic 
material, since all the higher land around the lake is made up of 
volcanic rocks. Therefore the source of the boron is to be sought 
in the volcanoes. Unfortunately lack of time did not permit an 
examination of the craters themselves. But it is known that 
borates and free boric acid in the form of sublimates from hot 
vapors are often conspicuous deposits around fumaroles and active 
volcanic craters in various other parts of the world. Judd states 
that in the solfataras of Tuscany, boracic acid is, next to the true 
gases, the most noteworthy compound emitted from the vents. 
Vulcano, in the Lipari Islands, emits boracic acid which, attacking 
the materials of the surrounding rocks, has formed borates of the 
alkalies and alkaline earths.2 These new chemical compounds 
are continually accumulating on the sides and lips of fissures from 
which the acid gases and vapors are issuing. ‘The mineral sassolite 
(B,0,.3H,O) is common at Vesuvius. Compounds of boron are 
therefore to be expected in these Chilean volcanoes and it may be 
supposed that rain-water falling upon these craters and percolating 
through the cinder cones would dissolve the soluble boron salts 
and later deposit them on the lake bed where the water finally 
evaporated. 
But in addition to borates, other salts soluble in water, such 
as chlorides, sulphates, etc., are also present in volcanic craters. 
These should also be dissolved by rain-water and carried down 
onto the evaporating flat as well as the borates. This has evidently 
happened in the Ascotan field, for the percentage of borate varies 
tJ. W. Judd, Volcanoes, p. 216. 
2 Tbid., pp. 42-44. 
3J. L. Lobley, Mount Vesuvius, p. 321. 
