370 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



or trappean in look. Under the microscope it is seen to be the exact analogue 

 to a common fine-grained diabase except that a brownish-green hornblende 

 replaces the usual augite. The hornblende has been partly altered to a fibrous 

 condition, and has a pale greenish tint; but there is no evidence that augite 

 has ever been present in the rock. It was, of course, necessary to determine 

 whether the uralitic secondary product had been derived from pyroxene. 

 A careful study of the thin section has led to the_ conclusion that it rather 

 represents this clearly uncommon form of alteration from hornblende. In any 

 case, there can be no question that much original, green hornblende has in this 

 rock an in terser tal relation to the other essential, labradorite-bytownite. Text- 

 urally the rock bears the same relation to camptonite that diabase bears to 

 certain dike-gabbros in which the pyroxene crystallized before the feldspar. 



South of Trail the granodiorite is cut by many trap dikes which, unfor- 

 tunately, have not been studied microscopically. Perhaps such a study would 

 declare with certainty the age relations of the batholith and the various mem- 

 bers of the Rossland volcanic group. 



The Sutherland schist complex is cut by a number of dikes of hornblende- 

 biotite monzonite porphyry, which may be contemporaneous with the Rossland 

 latites and monzonite. 



True lamprophyre dikes are rare along the traverses made by the writer. 

 The minettes cutting the Pend D'Oreille phyllites and slates near the Columbia 

 and the Boundary line have already been noted. In the immediate vicinity of 

 the Rossland mines mica-lamprophyres are very common and have been studied 

 by Young and Brock. 



About one-quarter mile west of the forty-fourth mile-post on the railway 

 between Coryell and Cascade, a four-foot, porphyritie dike of camptonitic habit 

 cuts a second dike of gabbro which itself cuts a volcanic breccia belonging to 

 an old member of the Rossland volcanic group as mapped (though probably 

 pre-Cretaceous in age). The younger dike is composed of beautifully crystal- 

 lized, idiomorphic crystals of green hornblende, augite, and plagioclase, 

 embedded in a microcrystalline. trachytic ground-mass of plagioclase and the 

 same femic minerals. Like the Coryell syenite the rock is very fresh and quite 

 uncrushed, and it may represent a rather acid camptonite which has been 

 derived from that batholith. 



Summary of Structural Relations in the Rossland Mountains. 



According to their degree of deformation the stratified rocks of these 

 mountains may be classified in three divisions. The first, characterized by 

 highly complex crumpling and by mashing, includes the formations of pre- 

 Mesozoic age; all of them seem to be Paleozoic, as there is no suggestion any- 

 where of the occurrence of a pre-Cambrian terrane in the Rossland mountains. 

 The second division includes the flows, pyroclastics, and interbedded sediments 

 of the Rossland volcanic group, which have usually high dips but lack the 

 chaotic structure due to orogenic mashing. The third division covers only the 

 various patches of conglomerate and sandstone, mapped on Sophie mountain, 

 Lake mountain, etc.; the dips of these beds may be locally high but on the 



