Letter from Dr Oudney to Professor Jameson . 883 
Near where we entered the valley, there is a cluster of date- 
palms, and a small lake, from which impure trona is obtained. 
On the western side is the trona lake, surrounded by date-trees, 
and its banks and marshy borders covered, on almost all sides, 
by the grass I have mentioned, and a tall j uncus. It is about 
half a mile long, and nearly 200 yards wide, of very inconsi- 
derable depth at present (July), from the evaporation of the 
water, and many places are dry now which are covered in the 
winter and spring. The trona is deposited in cakes at the bot- 
tom of the lake, when the saturation is at a certain extent. The 
cakes are of various degrees of thickness, from the finest film to 
several inches. The thickest I could find was not more than |ths 
of an inch, but at the beginning of winter, when the water be- 
gins to increase, it is of the thickness I have mentioned, and it 
is then said to be ripe. The surface next the earth is not un- 
equal from crystallisation, but rough to the feel, with numerous 
rounded asperities. That next the water is generally found 
studded with small beautiful cubical crystals of muriate of soda ; 
the line of junction is always distinct, and the one is easily re- 
moved from the other. The upper surface, when not covered 
with the muriate, is composed of a congeries of small tabular 
pieces, joined in every position ; when the mass is broken, there 
is a fine display of acicular crystals, often radiated. The sur- 
face of the water is covered in many places with large thin sheets 
of a carbo-muriate of soda, giving the whole the appearance of 
a lake partially frozen over : film after film forms, till the whole 
gets of considerable thickness. The soil of the lake is a dark 
brown sand, approaching to black, of a viscid consistence, and 
slimy smell, and on the lately uncovered surface, near the banks, 
a black substance, like mineral tar, is seen oozing out. 
The water begins to increase in the winter, and in the spring 
it is at the maximum. The trona is best about the commence- 
ment of winter, but disappears entirely in the spring. 
The lake has diminished considerably in size within the last 
few years, and if care be not taken, the diminution will soon be 
much greater : plants are making rapid encroachments, and 
very shallow banks are observable in many places. On inquiry, 
we found the quantity of trona had not sensibly diminished for 
the last ten years ; perhaps it may appear so, from there always 
