GEOLOGICAL ANTIQUITY OF GRANITE. 221 



first type or muscovite granite comprises granites formed of quartz, 

 orthoclase, minute and unimportant crystals of plagioclase, and mus- 

 covite, with a small percentage of microscopic apatite. This granite 

 lies to the west of Reese river, long. 117 W. It is seen in Nevada, 

 in the Kavenswood hills, in the Shoshone range, in the Pah-tson 

 mountains, in the Truckee range. 



The second type or biotite granite consists of quartz, orthoclase, 

 little or no plagioclase, and biotite, with microscopic apatite. It is 

 seen in the Ombe range, west of Salt Lake, in Nannie's Peak in the 

 Seetoga range, at Mount Tenaho in the Cortez range, on the Wah- 

 weah mountains, in the Montezuma range and in the Truckee range, 

 where it is associated with the muscovite granite. 



The third type or hornblende granite consists of quartz, orthoclase, 

 little or no plagioclase, biotite and hornblende, with microscopic 

 apatite. Its distribution corresponds very much with that of the 

 biotite granite, with which it is often in close proximity. It is well 

 seen in Granite Canon in the Cortes range, and at Granite point in 

 the Augusta mountains. 



The fourth type or plagioclase granite consists of quartz, plagio- 

 clase, orthoclase, and a large percentage of biotite, hornblende, tita- 

 nite, and apatite. The plagioclase often equals and sometimes exceeds 

 the quantity of orthoclase. Such a granite approximates towards the 

 diorites. 1 



Geological Age of Granite. The age of granite is always newer 

 than the rock which it penetrates, and older than a stratum deposited 

 upon it. It is rare to be able to fix both of these limits of age. 

 ]>ut the more ancient or Silurian granites are found in the Harz, 

 Thuringerwald, Saxon Erzgebirge, Yosges, Christiania in Norway. 

 The granite of Cornwall and Devon is of post-carboniferous date, as 

 also that of Arran. The protogine granite of the Alps is newer than 

 the Lias. And at Predazzo in the Tyrol there are granites of 

 secondary age, and other instances have been quoted near Champo- 

 leon in France, of granite overlying and altering secondary lime- 

 stones. In the Pyrenees both Liassic and Cretaceous limestones are 

 altered by contact with granite. In the Banat the granite is of 

 tertiary age, and similar examples are quoted by Darwin in Chile, 

 and Sawkins in Jamaica. 



Syenite. 



Syenite is a kind of granite which is typically free from quartz. 

 Orthoclase is the predominant mineral, and is associated with horn- 

 blende, biotite, and augite in proportions which vary with the locality. 

 When muscovite appears it is always as a secondary product, due to 

 decomposition of the orthoclase. The minerals in syenite are arranged 

 in the same way as in granite. 



The orthoclase in large-grained syenites is often rich in colour- 

 less microliths and small plates of specular iron. Sometimes fluid 

 1 Clarence King, TJ. S. Geol. Explor., 4Oth Parallel, vol. i 



