484 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



formably overlying detrital rock ; and this would hold good not only of 

 the intercalated beds, but also of the AYesteru sandstone. All these 

 evidences of denudation would then be merely signs of sequence of time, 

 and not of a difference in geological age. Precisely similar facts may 

 be observed at the present day wherever a lava flow has an opportunity 

 to reach the shore of the sea. 



The question, then, whether the copper-bearing rocks are a formation 

 of a geological age older than the Lake Superior sandstone, is to be 

 ascertained, if at all, on the eastern, and not on the western side. It 

 has just been pointed out on what evidence the Eastern sandstone was 

 said to be younger than the traps ; but a careful examination of the 

 region in question showed its incorrectness. At the Douglass Houghton 

 Falls the stream passes over a cliff of trap, and then winds through a 

 gorge having high and very steep banks. It was very natural that, in 

 ascending this stream from Torch Lake to the Falls, the hasty observer 

 should be led to believe that the sandstone and conglomerate extend in 

 an unbroken band up to the cliff at the latter locality, and regard it as 

 an old sea-shore bluff. This would especially be the case should he 

 confine his observations to the stream, and not attempt to explore the 

 clayey, slippery, difficult sides of the ravine. The writings of previous 

 observers give no evidence that they did more than to follow the bed of 

 the stream ; and they all concurred in stating that the sandstone was 

 horizontal, or nearly so, up to the Falls, at which place the trap was said 

 to be first met. When Dr. Wadsworth examined the locality, in 1879, 

 he not only explored the bed of the stream, but also the bluffs on both 

 sides. These examinations showed that the sandstone and conglomer- 

 ate were not horizontal, but that they had a gradually increasing dip as 

 the Falls were approached from 5° up to 25°, while on both sides of the 

 stream the ti'aps were found holding the same relations to the sand- 

 stone and conglomerate that they have been stated to hold elsewhere in 

 the series. These traps had been masked and concealed by the falling 

 rock and earth ; but, on digging, foot after foot of the junctions of a num- 

 ber of the lava flows and their adjacent sandstones were exposed. The 

 flow nearest Torch Lake is about two feet in thickness, lying between 

 two beds of sandstone, all having a dip of 20'^. Junctions of these beds 

 and the flow were exposed by excavating along a distance of about 

 twenty feet. The trappcan pebbles seen by former observers at the 

 Falls were seen to have been derived from the underlying trap, as they 

 are throughout the entire series, and not from the supposed old sea- 

 shore bluff. In the same way, the sandstone and conglomerate were 



