GRANITE ROCKS OF BOTTE, MONT. AND VICINITY F477 
rarely a coarse pegmatite. There is sometimes a banding with 
alternations of fine and coarse-grained material. 
The commonly accepted theory of the origin of aplite is 
that it represents the acid remainder in a granite or quartz- 
diorite magma after the more basic elements have crystallized. 
At a late period, after the main mass of the granitoid rock had 
crystallized, the aplite is forced up from below and fills previously 
formed cracks, which are perhaps the result of cooling. Viewed 
in this light they are genetically related to the more basic 
granites with which in the Sierra Nevada they are for the most 
part directly associated." 
The aphte-——The following calculation of the mineral com- 
position of the aplite, column I, is based upon the complete 
chemical analyses given in the table. A little biotite is found in 
the fresh aplite. This is similar to that of the granite and is 
supposed to have the same composition, and all the magnesia is 
ascribed to this. This leaves an excess of 0.09 of TiO,, which 
is calculated as titanite. 
I i! 
Quartz - 3 = : 37-70 39-45 
Potash feldspar - - = 333.00..." 29.43 
Soda feldspar - - - Bro 23°03 
Lime feldspar - - 2.45 6.56 
Biotite - - - - 0:72 .9O 
Magnetite, etc. - - Sy exo 58 
Titanite  - - - - 0.22 18 
100.00 100.00 
In column II the mineral compositions of the aplites of the 
Granodiorite of the Sierra Nevada, given by Turner, are given 
for comparison. 
LAMPROPHYRIC CONTACT FACIES 
The first two analyses in the large table represent the compo- 
sitions of two lamprophyric contact facies of the batholith. The 
rocks probably grade into the granite, though the transition is a 
TH. W. TURNER: Geology of Sierra Nevada, p. 722. 
