368 FRANCIS PARKER SHEPARD 



to be pre-Cambrian. Walcott^ believes that between these two 

 formations there is an unconformity, shown by the following: 

 (i) The overlying conglomerates contain fragments of the Hector 

 shale. (2) Slight hollows in the Hector shale are filled with thin 

 sandstone lenses. (3) The underlying Beltian (Proterozoic) 

 formation varies in character at the contact from place to place. 

 (4) The sediments seem to change from brackish water in the 

 Beltian, to marine in the Cambrian. (5) Allen's discoveries of 

 the contact between the Hector shale and the Fairview formation 

 showed apparent conformity in one place, while in two others 

 discordance of dip of 4°. 



Daly makes the following reply to these arguments: (i) The 

 fragments of the Hector shale in the overlying Fairview conglom- 

 erate are all angular and do not show a significant time break. 

 (2) The Fairview is nearly identical with formations occurring 

 at various horizons in the pre-Cambrian. (3) The sandstone 

 beds in the upper surface of the Hector are merely lenses which 

 are common elsewhere in the Beltian. (4) The discordance of dip 

 seen between the Hector and the Fairview can be explained by 

 irregularities in uplift as such are seen in continuous sedimentary 

 series in many locaKties. (5) The Selkirk series is divided on 

 lithological grounds into Cambrian and pre-Cambrian with the 

 dividing plane in the Ross quartzite, where there is no sign of 

 unconformity. 



Daly's first four points appear to be sound. Walcott's argu- 

 ments for an unconformity lack proof that a time break is repre- 

 sented. There might well have been a change in the conditions 

 of sedimentation without unconformity. In the natural order of 

 clastic sedimentation it is to be expected that there will be some 

 stirring of older sediments by changes in the activity of the cur- 

 rents. In the "clastic series" along the west side of the trench 

 many examples of such disturbances are found. It seems that 

 more evidence is necessary here to warrant the conclusion of an 

 unconformity of importance between the two systems. Minor 

 disconformities are of course present in great numbers in most 

 thick sedimentary series, especially if there are clastic sediments. 



' C. D. Walcott, Smithsonian Misc. Coll., Vol. LVII, p. 343. 



