74 



The city of Phoenix is 118-5 miles (190 km.) distant 

 by rail from Nelson, and is 4,600 feet (1402 m.) above 

 sea level. The city lies well within the Midway mountains, 

 a subordinate group of the Columbia system characterized 

 by comparatively low summits which show a uniformity 

 of crest line and they are below the limits of intense alpine 

 erosion. 



General Geology. 



The oldest rocks are of Palaeozoic age and correspond 

 largely to the Rossland group, a complex of igneous 

 rocks with minor developments of sedimentary types. 

 The structure is very complicated and there is an entire 

 absence of broad or continuous folds. The Mesozoic 

 batholithic intrusives and the consequent crustal dis- 

 turbances have added to the obscurity of formational 

 relationships. After the Laramide revolution the early 

 Tertiary was characterized by disorganized drainage and 

 vigorous erosion with sedimentation (Oligocene) in the 

 broader basins and with contemporaneous volcanic activity 

 accompanied by later warping and faulting. The later 

 Oligocene and Miocene lava flows were widespread. They 

 were followed by a period of erosion which developed a 

 mature topography with local base levelling followed 

 by uplift. The whole area was further modified by the 

 Cordilleran ice sheet. 



Table of Formations. 



Quaternary. 



Glacial and Recent. 



Clay, sand, gravel. 



Tertiary 



Miocene 



Oligocene 



Pulaskite porphyry, Augite por- 

 phyrite, Midway volcanic group 

 represented at Phoenix by flows 

 of trachyte. 





Kettle river formation, Con- 

 glomerate, sandstone, shale. 



Mesozoic 



Jurassic (?) 



Batholithic intrusion, represented 

 at Phoenix by augite syenite 

 and sj'enite porphyry dykes. 



Palaeozoic .... 



Carboniferous ? 



Attwood series. 



Rawhide formation. 



Brooklyn formation. 

 Knob Hill group. 



