Chap. VII. MINERALOGICAL ANTS. 537 
may be that these different causes combine to produce 
the result. 
The origin of the extensive gypsum formation in these 
parts, is in many places distinctly traceable to carbonate of 
lime. It is enclosed by limestone forming banks com- 
posed of large quantities of loose or slightly attached shells. 
I may here mention that I found a specimen of gypsum 
containing grains of gold in a collection of minerals at Los 
Angeles. The grains were rounded, and in all probability 
originally belonged to an alluvial deposit of detached frag- 
ments of carbonate of lime, which had been converted 
into gypsum by sulphuric acid. The gypsum with the 
alluvial gold may therefore be called a metamorphic 
alluvial formation. That with the alluvial gold was found 
on the Tejon Pass. 
Before continuing the account of our journey I must 
offer a remark here, connected with an observation I made 
in the desert. When traversing certain parts of the North 
American steppes and deserts I have frequently observed 
ant-hills, formed exclusively of small stones of the same 
mineral species, as for instance, small grains of quartz. In 
one part of the Colorado Desert the hills of these mineralo- 
gical ants consisted of heaps of small shining fragments of 
crystallized feldspar, chosen by these little animals from the 
various components of the coarse sand of these parts. The 
last time I was at El Paso, a North-American driver came 
to me and inquired the value of a small bag of garnets 
he possessed. On my asking in what place they had been 
found, I heard that these stones — imperfect crystals of red 
transparent garnets — were the material of which the ants 
build their hills in the country of the Navajo Indians, in 
New Mexico, and that he knew a place where any quantity 
of them might be collected. These remarks may perhaps 
