CENTEAL AND EASTEEN NEVADA. 325 



tlie product of a later metamorpliism, has also been left undesignated by any 

 distinctive color. 



Volcanic rocks. — These rocks are not known to occur earlier than the 

 tertiary period; those found in this range may be referred to the two varie- 

 ties, propylite, the earliest of the volcanic series, and rhyolite, generally con- 

 sidered to be among the most recent, though here it has directly succeeded 

 the propylite. Both of these rocks have played an exceptionally important 

 part in the structure of this range, since they usually occupy oro graphically a 

 subordinate position. 



Propylite. — Both hornblendic and quartzose varieties of propylite are 

 found in each of the two localities of this rock in the range, but, compared 

 with other bodies in the State, they are very rich in silica. 



Rhyolite. — This rock, usually noted for its great variety of texture and 

 color, though it occurs here in exceptionally large masses, is of comparatively 

 uniform texture; it is generally of the crystaUine or granitic variety, the 

 occurrence of the porphyritic, hyaline, and earthy texture being of subordi- 

 nate importance. 



The quaternary formations are represented by the extensive accumula- 

 tions of detrital material, which cover the sloping sides of the adjoining val- 

 leys, varying from a coarse gravel, inclosing occasional large rock fragments, 

 to a fine, almost impalpable, silt. The gravel benches of the park basin may 

 be referred to the same period. 



Structure of the Eange. — The geological formation of this range, 

 presenting as it does the result of upheavals, metamorphisms, and eruptions, 

 extending over long geological periods, affords the type of a most compli- 

 cated mountain structure, of which the present report can only claim to give 

 the general outlines. 



In its original elevation, as represented on the map by the stratified 

 rocks and granites, may be traced the result of the action of forces of con- 

 traction or compression^ acting in two directions, laterally, or at right angles 

 to the general line of elevation, and longitudinally, or parallel to that line. 

 The lateral, or main forces of upheaval, have produced antichnal and syncli- 

 nal folds, whose axes would have the general direction of the range. The 

 effect of the longitudinal compressions has been a disturbance of these condi- 

 tions, causing a deviation from the general direction, and a crumpling and 



