REPORT OF THE CHIEF ASTRONOMER 375 



SESSIONAL PAPER No. 25a 



Probable Relations. — The more detailed descriptions of the formations con- 

 tain statements of certain conclusions which can only be regarded as a fairly 

 strong" balance of probability in each case. A short summary of these views 

 will be of use in approaching- the final correlation. The evidences in their 

 favour will, for the most part, be found on earlier pages. 



1. The fern-bearing Mesozoic argillites and sandstones of Little Sheep 

 valley overlie the Paleozoic (Carboniferous?) limestone-chert-quartzite series 

 tmconformably and are overlain, with apparent conformity, by the Malde 

 mountain-Sophie mountain breccia (Rossland group). 



2. The conglomerates shown in the four mapped areas are equivalent in 

 age and are younger than some at least of the andesites and basalts of the 

 Rossland volcanic group, while perhaps slightly older than the latites. 



3. The monzonite porphyry dikes cutting the Sophie mountain conglom- 

 erate, the Beaver Mountain sediments, and the Little Sheep creek (Cretaceous?) 

 sediments are of the same age as the Rossland monzonite. 



4. The latites are genetically connected with the Rossland monzonite and 

 both are younger than the great mass of the Rossland andesite and basalt. 



5. The gabbros, the dunites, and other peridotites between Rossland and 

 the Christina lake-Kettle river valley are genetically connected with the 

 andesite-basalt (not greenstone) phase of the Rossland volcanic group. 



6. The syenite-porphyry dikes cutting the Sheppard granite south of Lake 

 mountain are the equivalents of the apophyses from the Coryell syenite 

 batholith. 



7. It i9 assumed that the last great orogenic revolution which has affected 

 this region was that at the close of the Laramie. Vertical to very steep dips 

 are taken, therefore, to mean that the rocks so deformed 'are of pre-Eocene age. 

 All the sedimentary formations and, so far as known, all the lavas and pyro- 

 clastics of the ten-mile belt often show dips which are much higher than those 

 characterizing, for example, the Oligocene beds west of Midway. Moderate 

 folding and faulting probably affected the Rossland mountains during or at 

 the close of the Miocene (as in the region west of Midway), but it has not 

 proved possible to distinguish the results of that deforrilation from those due 

 to the post-Laramie revolution. The Pend D'Oreille group and the other 

 (probably) Paleozoic sedimentaries of the region were doubtless more or less 

 deformed near the close of the Jurassic, when these rocks may have been 

 crumpled and mashed to a degree rivalling their present condition. 



8. The tentative correlation is partly based on the law that granitic (bath- 

 olithic) intrusion follows periods of more or less intense mountain-building 

 and seldom or never affects undeformed strata. The uncrushed Coryell syenite 

 batholith and its satellites, lamprophyres, and aplites are referred to the post- 

 Eocene orogenic period. The older, partially sheared but not greatly crushed 

 Trail batholith, the majority of the lamprophyric intrusions of the region, and 

 the greatly crushed biotite-granite stock east of Cascade are referred to the 

 late Jurassic period of deformation and intrusion. 



