424 
GLACIAL GEOLOGY 
on the surface of the lake waters and have settled to the bottom. 
Compared with desert deposits of other regions the white, marly 
upper beds of the section, which have such a variable thickness, 
are essentially what the Mexicans call calische. It is formed 
through ordinary soil tension by which lime salts of moist porous 
formations below are carried to the surface of the ground where 
the water evaporates leaving behind the solids. In some places 
there is sufficient lime deposited interstitially to give the beds the 
aspect of chalk. Upon further induration some layers pass into 
limestone. 
The juncture of the yellow and white beds is a sharp, irregular 
line that is easily mistaken for an erosion unconformity. That it 
is not at all probable that in the Bonneville Basin this line actually 
represents unconformable relationships between the beds above 
and those below is clearly indicated by the fact that the phenome¬ 
non is a common one throughout arid lands wherever porous 
formations reach sky. 
The yellow Bonneville clays do not appear, therefore, to repre¬ 
sent a deposit which was laid down during a high-water precursor 
of the high-stage Lake Bonneville; and the irregular line separat¬ 
ing the yellow and white sections does not stand for a long inter- 
lacustrine epoch, when the lake waters were completely desiccated, 
during a dry interglacial time. The white marls seem to be very 
recent in formation, produced directly from the yellow clays long 
after Bonneville waters had finally receded. Their especial cli¬ 
matic significance is manifestly very different from that formerly 
postulated. The ascribed pecularities seem to be really every-day 
phenomena. 
Keyes 
