REPORT OF TEE CHIEF ASTRONOMER 83 



SESSIONAL PAPER No. 25a 



The specific gravity of three specimens of the argillite ranges from 2-616 to 

 2-697, averaging 2-652. The average for the whole formation (including the 

 dolomitic interbeds (2-743) and the amygdaloid (ca. 2-900) is about 2-675. 



Thin sections from different specimens of the argillite show, under the 

 microscope, differences of grain but, in other respects, are similar. Angular, 

 sherdy grains of clear quartz and of notably fresh microcline and microperthite, 

 cloudy orthoclase, and a little indeterminable plagioclase lie embedded in an 

 abundant cement of apparently true argillaceous matter, reddened with much 

 hematite. Grains of magnetite and apatite, probably of clastic origin, are 

 present. Ragged foils and shreds of sericite developed in the bedding-planes, 

 and secondary kaolin represent some recrystallization, but the rock must be 

 regarded as a true argillite. In none of the thin sections does it show the 

 amount of recrystallization seen in the older, more deeply buried metargillites. 

 In one section, minute, pale brown grains of carbonate, probably dolomite or 

 ferrodolomite, are distributed as in the Grinnell metargillite. 



The recurrence of the special feldspar, microperthite, in the Kintla sedi- 

 ments — a constituent which is found in most of the clastic beds through the 

 whole Lewis series — shows that probably one great crystalline terrane furnished 

 the detritus during the deposition of the series. The great freshness of the 

 feldspars in most of the beds suggests that the erosion of that terrane and the 

 process of sedimentation were rapid. One may well suspect also that the 

 climate in which disintegration overtook chemical weathering was an arid 

 climate. This suspicion is strengthened by the discovery of abundant casts of 

 salt-crystals in the Kintla rocks. Barrell has shown reasons for believing that 

 the Kintla rocks were laid down under continental conditions, as subaerial 

 deposits.* For this one formation the writer can quite agree with the view, 

 but he believes that the Sheppard and all the underlying formations, excepting, 

 possibly, a limited thickness of Grinnell and Appekunny beds, were laid down 

 on the sea-floor. 



ABSENCE OF TRIASSIC AND JURASSIC FORMATIONS. 



No strata referable to the pre- Cretaceous Mesozoic occur within the 

 Boundary belt either in the Clarke range or in any of the other ranges between 

 the Great Plains and the Columbia river. In his reconnaissance of 1875 

 Dawson assigned the red beds of the Kintla formation to the Triassic, basing 

 his correlation on the lithological similarity of the argillite-sandstone to the 

 Triassic of the states farther south, and on the belief that the underlying 

 Siyeh limestone is of Carboniferous age.f Willis has concluded that the 

 Kintla formation is much older than the Triassic and, as indicated, the present 

 writer agrees in assigning a pre-Devonian age to the formation.:}: 



*.T. Barrell, Journal of Geology, Vol. 14, 1906, p. 553. 



t G. M. Dawson, Bull. Geol. Soc. America, Vol. 12, 1901, p. 74, \rhere further refer- 

 ences. 



J B. Willis, Bull. Geol. Soc. America, Vol. 13, 1902, p. 325. 



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