GEOLOGICAL REPORT. 329 



other points. Some of them are closely allied to the trachytic porphyries from Carson 

 River and Ragle Valley, on the east side of the Sierra, Nevada; others ean scarcely 

 be distinguished from some of Weber River, and others again present quite* a peculiar 

 appearance. In this neighborhood the Great Salt Lake and Sevier Lake deserts con- 

 nect with such a scarcely perceptible change of slope, that avc are frequently at a 

 loss to tell whether we are in the one or the other. 



Colonel Thomas's range, at Pass Short-cut, is composed of stratified rocks, proba- 

 bly of Carboniferous age, which are tilted, as well as covered, by an overflow of a 

 trachytic. porphyry of gray color. Some strata are thereby highly altered; sand- 

 stones have attained a porphyritic appearance, by a beginning secretion of quartz in 

 single crystals, as in a porphyry. Farther to the south, near the pass on our return 

 trail, the igneous rocks prevail, and only a few highly-altered limestones were noticed. 

 and some layers, in regard to which I was doubtful whether they were originally 

 eruptive or sedimentary. One of the most common rocks there has a peculiar mod- 

 ern appearance, in consequence of its more loose texture. In a gray matrix it contains 

 a great deal of transparent quartz, very brittle and partly crystallized in perfect double 

 hexagonal pyramids, also white glassy feldspar and a little black mica. It has some- 

 what the appearance of trachytic lava, but is closely allied to the rocks from Mount 

 ( 'hamplin. ( Mlier varieties have a grayish white or very light pink matrix, containing 

 only few and small crystals of the same minerals, which makes them look vastly dif- 

 ferent; probably in consequence of a beginning decomposition, or the mode of cool- 

 ing to which they have been subject, they shell off in rounded masses, forming pecu- 

 liar knobs, or, if the inner part has been worn out, cavities of various size. 



Next follow the House Mountains, which extend from Sevier Lake northward, 

 and are lost in the Salt Lake desert. As far as they have come under my observation, 

 they are entirely composed of stratified rocks, dark-colored siliceous limestones, com- 

 pact sandstones, and slates. Some of them are highly altered. Only a fragment of a 

 Trilohitc, apparently of a Carboniferous species, was found near Chapin Spring, and 

 the lithological character of the rocks there points to the same age. Near the north 

 end of this chain the remarkable Fish Springs are found, and not far from them, along 

 the foot of the mountains, horizontal strata of a white calcareous marl, in appearance 

 much like chalk, which must have been deposited in the ancient lakes, and to the form- 

 ation of which infusoria? seem to have contributed largely. Near there, 1 also noticed 

 a water-mark of calcareous tufa lining the mountain-side for a considerable distance. 

 Highly altered stratified rocks also form the main portion, at least, of the hills between 

 this range and the Goshoot Mountains. 



The Tots-arrh or Goshoot Mountains are one of the principal ranges of great 

 length and altitude. Their main body consists of stratified r< >cks, limestones of mostly 

 bluish color, sandstones and slates, which form some of the highest peaks, among 

 them Mount Davis. In the pass from the desert to Pleasant Valley, some fossils of 

 Lower Carboniferous age were found, and also near our camp on the western slope. 

 Many of the strata are strongly altered, sandstones converted into quartzite, &c. Be- 

 sides, we find some metamorphic rocks, mica schists, argillaceous slate, gneiss, and 

 even granite ; but I have not seen any of the porphyritic and other more recent lgne- 

 42 b u 



