292 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



Basic segregations, in the form of deep green to black ellipsoids from five 

 centimetres or less to ten or fifteen centimetres in diameter, are quite common. 

 These small bodies are of two classes. In the one class the essential components 

 are hornblende, labradorite (Ab 4 An 3 ), biotite, and augite, named in the order 

 of decreasing abundance. A little quartz and orthoclase, with much crystallized 

 titanite, magnetite, and apatite are accessory. Microperthite and microcline 

 seem to be entirely absent. The specific gravity of a typical specimen is 2-924. 

 In the other class of segregations the colour is yet deeper and is explained by 

 a complete lack of feldspar. The essentials are hornblende, biotite, and augite, 

 also named in the order of decreasing importance. Quartz is accessory but is 

 considerably more abundant than in the first-mentioned class of segregations. 

 The other accessories are titanite, apatite, and specially abundant magnetite in 

 crystals and rounded grains. The specific gravity of a typical sample is 3-214. 



There can be little doubt that all these bodies are indigenous and that the 

 segregation of the material, if not its actual crystallization, took place in the 

 early stage of the magma's solidification. 



The granodiorite is generally massive and uncrushed. Straining and 

 granulation through pressure were not observed in any of seven thin sections 

 cut from the specimens collected. Sometimes, though rarely, thin partings in 

 the granodiorite carry much biotite, which is arranged with its lustrous foils 

 lying in the planes of parting, as if there developed as a result of shearing- in 

 the crystallized batholith. At the Bayonne mine the rock is sheeted and locally 

 sheared. On the whole, however, the batholith is notably free from evidences 

 of dynamic disturbances and appears never to have suffered the stresses incid- 

 ental to an important orogenic movement in the region. 



As regards its influence on the intruded formations the Bayonne grano- 

 diorite has typical batholithic relations. A glance at the map suffices to con- 

 vince one that this huge mass is a cross-cutting body. Four of the thickest 

 members of the Summit series are sharply truncated by the main southern 

 contact. For distances ranging from one to two miles from that contact the 

 rocks of the Wolf, Monk, Irene Volcanic, and Irene Conglomerate formations, 

 are greatly crushed, fractured, and metamorphosed by the energetic intrusion. 

 Farther to the eastward, for a distance of ten miles down the Dewdney trail, 

 the schists and interbedded quartzites of the Priest River terrane, though 

 likewise truncated, have been almost completely driven out of their regional 

 strike and a well developed schistosity peripheral to the batholith has been 

 found in these recrystallized rocks. For the lower twelve miles the east-west 

 Summit creek canyon has been excavated along the strike of the schists, which 

 have been forced out of .their originally meridional trends by the force of the 

 intrusion. Abundant apophyses of the batholith sometimes 300 or 400 yards 

 in width, cut these various invaded formations. The main contact is sinuous 

 but clean-cut. Inclusions of the invaded rocks are not common in the bath- 

 olithic mass as studied in the ten-mile belt. 



