REPORT OF THE CHIEF ASTRONOMER 107 



SESSIONAL PAPER No. 25a 



These figures cannot, of course, represent the actual composition or " mode ' 

 oi the rock excepting as regards the carbonates. The calculation has some 

 value, however, in facilitating the chemical comparison of the molar-tooth 

 rock in the Galton series with that in the Lewis series, A reference to the table. 

 col. 2, showing the ' norm ' of the latter rock, indicates how nearly equivalent 

 the two rocks are in chemical composition. In both cases we are dealing with 

 a silicious, strongly dolomitic limestone of peculiar history and structure. 



In analysis B an appreciable amount of carbon was determined; here 

 again the carbonaceous matter largely controls the dark tint of the fresh molar- 

 tooth rock, which decolourizes before the blow-pipe. 



The specific gravity of three specimens of the molar-tooth rock varies from 

 2-670 to 2-748; that of four specimens of the metargillites in the formation, 

 from 2-630 to 2-739. The average of all seven specimens is 2-700. 



Gateway Formation. 



A striking difference in the lithological character of the Lewis and Galton 

 series is to be found in the nature of the beds conformably overlying the 

 Purcell Lava in the respective ranges. We have seen that, in the Clarke and 

 Lewis ranges, the Sheppard formation, occupying this position, is a homogene- 

 ous silicious dolomite and that it is overlain by the red beds of the Kintla. 

 In the Galton range the beds intervening between the Purcell Lava and the 

 red beds, equivalent to the Kintla, have a much greater total thickness than 

 the Sheppard and a quite different composition. These strata are well exposed 

 on the heights east of Gateway and overlooking Tobacco Plains; they may be 

 grouped under the name, Gateway formation. Its total thickness was found to 

 be about 2,025 feet. It includes two members of unequal strength. 



The lower member resting immediately upon the Purcell Lava contains 

 beds which at once suggest possible identity of origin with the Sheppard. This 

 correlation is so important that a specially detailed columnar section of the 

 member is here noted. It was made on the basis of field sections along good 

 exposures north of Phillips creek. 



Columnar section of Gateivay formation (lower part). 



Top, base of 1,850-foot member. 



5 feet. — Massive, light gray dolomite, weathering buff and brown. 

 4 " Massive, light gray quartzite. 



6 " Light gray magnesian and ferruginous limestone, weathering rusty brown. 

 10 " Thin-bedded, light gray quartzite. 



6 " Highly silicious, gray metargillite. 

 4 " Thin-bedded, gray dolomite weathering buff. 

 20 ' Thick-bedded, hard, light gray, often cross-bedded and ripple-marked 



quartzitic sandstone. 

 20 ' Thin-bedded, concretionary, light gray dolomite, weathering strong buff and 



brown. 

 50 ' Massive, dark gray, coarse, feldepathic sandstone, bearing locally lenses of 



grit and fine conglomerate one to two feet thick. 



125 feet. 



Base, conformable top of Purcell Lava 



