GEOLOGICAL REPORT. $03 



If we take in account also the rugged and precipitous character of its mountains, 

 naked, or scantily covered with a growth of stunted timber, and the monotony of the 

 expansive valleys, with their dreary sage-barrens, the picture of the country is com- 

 plete. 



IGNEOUS BOCKS. 



We find in this district igneous rocks of various description: granite rocks, dio- 

 ritic porphyries, tracln tic porphyries, trachyte (:'), phonolitic recks, greenstone, basalt, 

 pitclistone, lavas, obsidian, pumice, and numerous intermediate forms. They exhibit 

 a close alliance with formations beyond the limits of the Great Basin, in the Sierra 

 Nevada, the Coast ranges, the Colorado Basin, and portions of Eastern Utah. 



The systematic grouping of the igneous rocks, according to their analogous com- 

 position, the different minerals which they contain as essential and accidental compo- 

 nents, and their mode of aggregation, forms an instructive branch of geology, because 

 all plutonic rocks formed within certain, mostly extensive, periods and limits generally 

 bear evidence of it in their composition. They are similar to each other, and belong 

 to the same group, the more so the nearer they approach each other geographically, 

 originating from the same hearth. The history of the igneous rocks of a region, and 

 their relation to the stratified rocks of the different formations, form as essential a part 

 of the geology of a country as the history of the extinct organic life: both together 

 only make the whole. 



This department of geology has hitherto been much neglected, because no satis- 

 factory system of classification has ever been fully established. Still, several most dis- 

 tinguished mineralogists and geologists have led the way in Europe, especially Prof. 

 G. Rose, of Berlin. One of the principal obstacles to the study of the igneous rocks 

 is the necessity of numerous and difficult analyses of the feldspathic minerals, which 

 are of primary importance for a systematic classification. An omission in this respect 

 led some of the most noted geologists to make different statements in regard to the 

 composition of the rocks from one and the same locality, and, again, to use the same 

 name for differently composed rocks. 



This branch of geology seemed to require special consideration, in a country where 

 a variety of igneous rocks predominate, but it was impossil 

 rial from a hurried examination along the route, the more sc 

 all belong to a few of the older formations, and are, thereto 

 by all the more recent protrusions of igneous rocks, howex 

 age of these may be; nor have I had time and means to stuc 

 and make the necessary analyses, still less to compare them 

 tries. From a preliminary examination of the large number of specimens, over 160, 

 I have formed some conclusions which I give below, and which we submit for further 



The granitic rocks within the limits of my observations may be readily distinguished 

 from all other igneous rocks of the district. They are the oldest, and do 



o gather sufficient mate- 



cause 



• the stratified rocksv 



.fleet 



ed in the same way 



ditiel 



-ent the respective 



lies,)- 



ccimens sufficiently 





►se from other conn- 



of the others. They form the bases of some ot tli 



I found them in the Wahsatch Mountains, near longitude 11 



•ominent mountain 



tude 40° 27'; in the Gosh< 





