19 



is a grey medium grained, usually massive, but occasionally 

 coarse, gneissoid rock, intermediate in character between 

 the diorites and granites, and classed generally as a 

 granodiorite. Inclusions of fragments and even large 

 areas of the intruded rocks are common in them. 



Along the Skeena river, the Coast Range section is 

 made up of wide bands of light and dark grey granodiorites, 

 alternating with bands of dark basic schists, the largest 

 six miles (9.6 km.) across. The granodiorites in this section 

 show a more or less pronounced gneissic structure every- 

 where. Along their western margin the schistosity con- 

 forms generally in dip and strike with that of the bordering 

 easterly dipping altered sedimentaries. Farther on, the 

 direction and angle of dip varies from point to point, and 

 in a few places the lines of schistosity are sharply plicated. 

 The gneissic structure is considered to have been assumed 

 during the cooling of the granitic magma, and not to be 

 a product of subsequent dynamic deformation. 



In the Skeena section there is no clear evidence of 

 more than one period of intrusion, and the granodiorites, 

 except for slight differences in coloration and an occasional 

 banded arrangement due to a concentration of the dark 

 minerals, have a very uniform character across the range. 

 They are medium to coarse grained rocks, occasionally 

 showing a porphyritic texture, made up of a plagioclase 

 feldspar, usually andesine, orthoclase, microcline, quartz, 

 and either or both biotite and hornblende. Apatite, 

 titanite, and magnetite are common accessories, and 

 epidote and, less frequently, pyrite and garnet are con- 

 spicuous secondary minerals. The following table by 

 F. E. and C. W. Wright [8 p. 64] shows the mineral com- 

 position of the average batholithic rocks in the Coast 

 range in southeastern Alaska. 



Quartz 19-4 



Orthoclase 6-6 



Andesine (Ab.56 An. 44 ) 47 • 4 



Hornblende 7-6 



Biotite 1 1 • 6 



Apatite -6 



Magnetite -9 



Pyrite • I 



Carried forward 94* 2 



34883—2* 



