ABCHEAN FOEMATIONS. 277 



must have been comparatively smooth and have presented no abrupt cHffs 

 or slopes which vi^ere too steep for a uniform deposition of sediment over 

 them. 



Bedding planes were frequently observed in the Archean in proximity 

 to its upper surface, perfectly parallel with and corresponding to the bed- 

 ding planes of the Cambrian quartzite immediately above it. As this dis- 

 tinctness of bedding planes occurs in granite as well as in gneiss and as in 

 general the bedding planes of the Archean, as seen on a large scale, are 

 almost invariably discordant with those of the overlying beds, it seems that 

 they must have been produced by the pressure of the superincumbent mass 

 of beds. 



The eruptive granite of this region is, in all cases, pre-Cambrian in age, 

 no instance having been observed of its intrusion into the rocks of any for- 

 mation later than the Archean. 



As regards the relative age of the rocks which form the Archean, the 

 little study that could be devoted to this subject goes to show that the anr- 

 phibolites, gneisses, granite-gneisses, and, probably, part of the granites 

 proper constituted the older or original formation ; that these were suc- 

 ceeded by the distinctly eruptive granites, which cut through and include 

 fragments of the above ; and that the vein-like masses of pegmatite are the 

 most recent formations of all the Archean rock masses. 



While the structure lines which give evidence of original bedding or 

 stratification in these rocks are less distinctly marked than in other parts of 

 the Archean of the Rocky Mountains and were often so obscure that no 

 attempts were made to trace out any structural system in the Archean as a 

 whole, the}^ are nevertheless sufficiently well marked to suggest an original 

 horizontality in the different layers, and that they have been subjected to 

 an infinitely greater compression and folding than the later formations, 

 while the parallelism of certain upper planes with the lower ones of the 

 Cambrian, which has been remarked above, and the varjing angle at which 

 both are found, show that the Archean has partaken of the folding to which 

 the Cambrian and later beds have been subj-ected. 



Paleozoic. — The lower 600 feet of the Paleozoic system in this region, 

 comprising the Cambrian, Silurian, and Lower Carboniferous formations, 



