162 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 

 Table I. — Correlation of the Rocky Mountain Geosynclinal rocks — Con. 



Summit series. 



PURCELL SERIES, 

 WESTERN PHASE. 



GALTON SERIES. 



Lewis series. 



Dewdney, 2000' 



Creston, 9500' + 



MacDonald, lower part, 



Appekunny, 2600' 



Quartzite, with conglo- 



Quartzite, with me- 



1650' 



Metargillite, with quart- 



merate. 



targillite. 



Metargillite, with a 



zite and a little dolo- 



Wolf, 2900' 





little dolomite. 



mite. 



Grit, with conglomerate 





Hefty, 775' 



Altyn, 3500' 



and sandstone. 





Sandstone, with quart- 



Silicious dolomite, with 



Monk, upper part, 2500' 





zite and a little me- 



dolomitic grits and 



Quartzitic sandstone, 





targillite. 



sandstone. 



with metargillite and 





Altyn, upper part, 650' + 



Waterton, 200'+ _ 



conglomerate. 





Silicious dolomite. 



Silicious dolomite. 



Monk, lower part, 3000' 









Quartz schist and phyl- 









lite, with conglome- 









rate. 









Irene Volcanics, 6000' 









Greenstone and green- 









stone schist, with a 









little phyllite and one 









bed of angular con- 









glomerate. 









Irene conglomerate, 









5000' + 









Coarse conglomerate, 









with sandstone and 









grit and a little inter- 









bedded greenstone. 









Basal unconformity. 



Base concealed. 

 Total, 20,765 feet. 



Base concealed. " 



Base concealed. 



Total, 32,050 feet. 



Total, 12,460 feet. 



Total, 13,720 feet. 



The most useful horizon is that of the Purcell Lava formation. Probably 

 no other geological horizon betokens contemporaneous events in distant locali- 

 ties more surely than such a lava flood. A sandstone bed or other product of 

 sedimentation on the floor of a transgressing sea may belong to more than 

 one geological period. A lava flood not more than a few hundred feet in thick- 

 ness at any point is, on the other hand, developed with comparative rapidity. 

 Even a great compound flood generally covers its whole field in but a small 

 fraction of a geological period. Essential contemporaneity thus characterizes 

 the surface of the sediments overrun by the Purcell Lava. Since the overlying 

 strata are apparently in absolute conformity to the lava and to the strata 

 underlying the lava, it is probable that several hundreds of feet of beds above 

 and below the Purcell Lava are likewise practically contemporaneous. Since 

 the lava formation has been traced from southeast of Altyn, Montana, and 

 from the heights overlooking Waterton lake at the Great Plains, all the way 

 to the eastern summits of the Purcell range on the Boundary, the value of this 



