104 GEOLOGY. 
not so constantly preserved as in the country east of the Wahsatch mountains, and the soil 
offers in many places, as far as its chemical composition is concerned, by far more resources. 
The slopes of the mountains west of the Humboldt mountains are dian covered with an ex- 
cellent soil, producing a good grass, and the want of a more luxuriant vegetation can only be 
explained by atmospherie and similar influences. 
The mountains on the west side of the Great Salt lake have their chief geological features in 
common with those on the east side. A dark limestone belonging to the coal formation, and 
above it a conglomerate, resting on porphyritic and granitic rocks, in some places on a silicious 
shale, constitute the materials out of which they are formed. This limestone as well as the 
conglomerate, or rather remnants of them, are occasionally met with in many other places 
travelling westward. The former is one of. the main rocks constituting the Humboldt mount- 
ains, where it overlies granitic masses. In the northern parts of this mountain range the granite 
passes gradually into quartz, the latter assuming in some places a shaly structure. It is 
through limestone that the waters of a subterranean creek in the Humboldt mountains have 
broken an outlet; and both limestone and conglomerate are often found on the summits of the 
highest peaks of those regions. A soft shaly rock has almost entirely disappeared from that 
country, and I found remnants of it only in one single place east of the Humboldt mountains; 
but the clayish soil, over which we had to travel for days, and which contained a number 
of small pieces of the rock, led to the belief that it extended once far over the country. 
The island mountains in the salt desert immediately west of Great Salt lake consist of granitic 
and porphyritie rocks; the latter is like most of the porphyries we met with, trachytic, its 
brownish base dissolving under a lens into small grains and broken crystals melted together. 
It includes numerous crystals of feldspar and grains of quartz, many half an inch thick, and 
is very hard. 
About a mile and a half from the eastern foot of the Humboldt mountains, about camp 19, 
(1854,) an interesting phenomenon is presented to the view by a number of warm springs— 
some forty—all of them lying in a circuit of about a hundred yards in diameter. They rise in 
tubular channels cut through the granite, most of them having a kind of funnel-shaped reservoir 
on the surface. The smell of the water and a deposit around the springs, show at once that 
they contain sulphureted hydrogen, and, although quite tasteless when cooled, the water con- 
tains, besides the sulphureted hydrogen, a slight proportion of chlorides and solplaton, as shown 
by chemical test. The temperature of the water on the surface is about 132° Fahrenheit. The 
spring we found afterwards in Honey Lake valley seems to have the same chemical composition, 
but its temperature is at the boiling-point. 
The mountains lying between the Humboldt mountains and Humboldt river, by our path, are 
chiefly composed of quartz rocks, trachytie or dioritic porphyry, the above-mentioned dark lime- 
stone and conglomerate, and a soft, white, argillaceous or calcareous sandstone. The most 
remarkable rock in that country, and which deserves a particular mention, is found around the 
gorge wé came through on the 2d of June, and for which I proposed the name of ‘‘Agate 
canon." This rock is a compact mixture of piri of the quartz family—agate, chalcedony, 
and jasper—and is evidently of igneous origin. To the practical arts it would offer a material 
which for beauty and hardness can hardly be surpassed. 
West of Humboldt river we find quartzose rocks, syenites, and granites, and a soft clay- 
slate, as the predominating rocks; but the nearer we approach to the Sierra Nevada, the more 
the so-called volcanic rocks take their place, and at last become the only constituent material 
of the mountains. In Mud Creek caiion, at the foot of the Sierra, we find for the last time a 
rock which, by its lithological character, is related to the rock I designated as trapp-porphyry, 
only that it has become shaly or foliating, by the influence of the surrounding volcanic rocks. 
In the neighborhood of that cañon I found a rock which has all the appearance of standing 
between this rock and the trachytes of these regions, and which seems to have been formed by 
the action of these rocks upon each other. 
