782 



DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



Period. 



Basalts, diabases or gabbros. 



Augite (pyroxene) andesites. 



Post-Miocene 



Mt. Baker lava ? 



Basalt dikes of Okanagan Range. 



Yakima basalt of Washington. 



Dawson's Upper Volcanic group 



of Interior Plateaus. 

 Basalt of Midway volcanic group. 



Teanaway basalt of Washington. 



Basalts of Rossland, Beaver 



Mountain, and Phoenix groups. 



Some gabbros of Columbia range. 



Rock Creek gabbro (age?) 



Diabases of Nicola group (Daw- 

 son). 



Diabases of Vancouver group 

 (Dawson). 



Basalts of Chilli wack formation. . 



Basaltic traps of Hozomeen, Anar- 

 chist, and Cache Creek series 

 (age?) 



Purcell Lava. 



Basalts of Irene Volcanic form- 

 ation. 



Diabase of Dawson's Adams Lake 

 series. 



Mt. Baker lava. 



Andesite of Wenatchee District 



(Washington) . 

 Porphyrite of tipper Volcanic 



group (Dawson). 

 Andesite of Midway volcanic 



group. 

 Andesite of Skagit volcanic group 



Andesites of groups named in 

 opposite column. 



Jurassic 



Triassic 



Porphyrites of Nicola group. 

 Porphyrites of Vancouver group 



Carboniferous 



Pre-Beltian 



Andesitic traps of Hozomeen, 

 Anarchist, and Cache Creek 

 series (age?) 



Andesites of Irene Volcanic 

 formation. 







4. The table also shows numerous examples of the common field- association 

 of pyroxene andesite, or porphyrite, with basaltic rocks. The writer has 

 assembled some of the facts which he regards as sufficient proofs of the deriva- 

 tion of this andesite from basalt, and has recently published a summary state- 

 ment of the case.* In that paper emphasis was placed on a differentiation 

 through the settling-out of ferromagnesian and cafemic crystals of early genera- 

 tion. But it was pointed out that a parallel effect might be produced by the 

 settling-out of the same constituents in the liquid phase, that is, by a kind of 

 liquation. Both actions comprise what has been called gravitative differ- 

 entiation. Without, then, attempting to decide which process has been dominant 

 in any case, we find in this general association of augite andesite with basalt 

 along the Boundary Line, a substantiation of the hypothesis that the andesites 

 have been derived from the more basic magma by gravitative differentiation. 

 The complementary differentiates, the peridotites, are also found in close 

 association with rocks of basaltic composition but, as to be expected, not so 

 often nor in such volume as the andesites. 



* R. A. Daly, Jour. Geol., Vol. 16, 1908, p. 401. 



