REPORT OF THE CHIEF ASTRONOMER 571 



SESSIONAL PAPER No. 25a 



expected to have preceded batholithic intrusion. So far, however, no Eocene 

 granites have been demonstrated. With doubt the intrusion of the Kruger 

 alkaline body in Kruger mountain has been referred to that period. 



13. The new, very strong topography produced by this Laramide upturn- 

 ing seems not to have permitted important sedimentation in the area of the 

 Boundary belt. A hundred miles to the south very thick prisms of fresh-water 

 beds were laid down in the State of Washington. The Tertiary formation of 

 Sumas mountain was probably part of the once continuous body of clastic 

 material carried into the Eocene geosynclinal of Puget Sound and the Gulf 

 of Georgia. This sedimentation was the reciprocal of extensive and profound 

 denudation in the Belt of Interior Plateaus. During the Eocene the Eastern 

 Geosynclinal Belt was, at the Eorty-ninth Parallel, eroded apparently through 

 its whole width. 



14. Judging by analogies from adjacent regions north and south, the Puget 

 Eocene geosynclinal area was, at the close of the Eocene proper, uplifted though 

 not strongly deformed. 



15. The Oligocene continued the erosive work of the Eocene over most of 

 each of the great Cordilleran belts. West of Midway, some of the detritus was 

 trapped during the sway of the local vulcanism, with the production of a 

 notable fresh-water series of sandstones, argillites, and conglomerates (Kettle 

 River formation). 



16. The early Miocene was also a time of general erosion all across the 

 Cordillera; only very limited fresh-water deposits were made. On the Forty- 

 ninth Parallel the only one referable to this date is that flooring the fault- 

 trough at the North fork of the Flathead river. 



17. Toward the close of the Miocene, the Oligocene fresh-water beds at 

 Midway were moderately upturned and eruptions of rhomb-porphyry, ' shacka- 

 nite,' trachyte, and pulaskite porphyry overwhelmed the older Midway lavas and 

 the Kettle River sediments. Probably at this time also the Eocene beds of 

 Sumas mountain far to the west were somewhat tilted and faulted; and the 

 more yielding Miocene clays and sandstone of the Flathead trough were strongly 

 deformed. It is possible that the Cretaceous rocks of the Pasayten district 

 were further disturbed, though we must ascribe their principal deformation to 

 the much more powerful crustal adjustments of the Laramide revolution. 



13. The Miocene deformation was closely followed by new extensive, batho- 

 lithic intrusions. These seem to be registered in the great Similkameen and 

 Cathedral batholiths in the Okanagan range; the Castle Peak stock of the 

 Hozomeen range; the Coryell syenite batholitb and its satellites of the Ross- 

 land mountains; and the large Bayonne batholith and its satellites of the 

 Selkirks. As abundantly indicated in the foregoing chapters, these correlations 

 are provisional only, and a date so recent for these great intrusive bodies is not 

 proved for any one of them. There can, however, be little doubt that all of 

 them are of post-Cretaceous age, following the Laramide revolution. 



19. The strength of the Cordilleran topography was doubtless considerably 

 increased by these late Miocene movements. Since then, both of its geosyn- 

 clinal belts have suffered steady erosion by river and glacier. The Pliocene 



