Reconnoissance in New Me.xico.—Johnson, 83 
one of the low rises and looked down into the basin, with its 
level floor covered with snow-white salt stretching far away to 
the south, did we realize that we were in the vicinity of the 
lakes. The lake bottom is usually from some thirty to fifty feet 
below plain level, or from fifty to one hundred feet below the 
top of the surrounding ridge. <A section of the side of one of 
these lake basins was as follows: 
5 Feet. 
Imperfectly stratified adobe soil (dune formation) 65 
Imperfectly, lithified shales ............c.sse00s0. 30 
Gradually sloping mud flat (to the edge of the 
ee aint cna tic Rin akon ak dae hu’ 10 0% I 
The upper soil, composing the embankments or dunes 
about the lakes, is not saline to the taste, and contains but little 
over 1% of sodium chloride. About a few of these lakes, es- 
pecially toward the south, these dunes are entirely lacking in 
places. As stated above, the underlying shales are strongly 
saline to the taste, and contain crystalline gypsum. The mud 
flats are often thickly strewn with fragments and small crys- 
tals of gypsum, to such’an extent that about the shores of some 
of the lakes the ants have built numerous large hills composed 
entirely of these fragments. 
As a rule most of these lakes are dry and covered with a 
thin crust of more or less pure salt. The Laguna del Perro, 
the largest of these lakes, is only dry in part, however, salt 
water standing in portions of it most if not all of the year. 
We secured samples of the white crust, to which some of the 
wet underclay necessarily adhered. Analysis of the saniples 
showed 76.6% salt.* This salt crust is of variable thickness, 
but will average about a quarter of an inch over the portions 
of the lake, dry at the time of our visit. About six inches below 
the surface crust was an inch layer of what appeared on first 
sight to be coarsely crystalline salt. Analysis showed 6% sod- 
ium chloride, the remainder being almost pure finely crystal- 
line gypsum. Clay from a foot and a half below the sur- 
face showed 6.1% salt. 
Unfortunately two terrific storms swept over the valley 
shortly after we left the Laguna del Perro, and as we jour- 
neyed along the ridges between the smaller lakes to the east. 
. *Percentage of salt based on chlorine determinations. 
