The Lake Systems of Southern Patagonia. — Hatcher. 171 
ual elevation constantly taking place, would tend to decrease 
the circulation between the waters of the bay and the ocean. 
By the combined action of these two agencies, the circulation 
would be more and more impeded until a stage would be 
reached in which this circulation would become intermittent. 
The two bodies of water would then be entirely separated, 
except during periods of unusually high tides, when the waters 
of the sea would rise sufficiently to overflow into the bay, or 
lake as it might now be more properly termed. At first the ob- 
struction would not be so great but that the bi-weekly high 
tides occurring with each full and new moon would produce 
a flow of water from the sea into the lake, thereby replenishing 
every two weeks the water lost by surface evaporation with a 
new supply of sea-water. After a time the obstruction would 
become so great that only the exceptionally high semi-annual 
tides would suffice for its submergence, and the replenishing 
of the waters of the lake would then occur only once every six 
months. After this a stage would be reached when ordinary 
spring tides would no longer suffice, and only an exceptionally 
high tide brought on by a continued strong easterl}' wind, act- 
ing in conjunction with the sun and moon at the period of 
spring tide, would pile up the waters of the sea sufficiently high 
to overflow the isthmus separating it from the lake. Such con- 
ditions would, of course, occur only at irregular intervals and 
would constantly become less and less frequent, until finally all 
communication would cease and the smaller body of water 
would become entirely separated as an inland salt lake, grad- 
ually diminishing in area after the last overflow, by evapora- 
tion from its surface until a point would be reached when the 
loss by evaporation would just balance the gain from tributary 
streams and springs, which latter, in the lakes in the region 
now being considered is exceedingly slight. 
It was during these stages of intermittent communication 
that the salt deposits were formed. These deposits are now 
found often covering the bottoms and adjacent shores of the 
lakes to a depth of several feet. During periods when com- 
munication between the lakes and the sea was suspended, the 
volume of water in the former would be greatly reduced b\' 
evaporation, thus increasing its salinity until an oversaturated 
solution would be attained, resulting in the precipitation of 
