Copper-bearing Rocks of Lake Superior. 431 
west of the lake these rocks end in steep and high declivities, 
at the base of which lies the level country of the Silurian sand- 
stone, in which is cut the basin of the lake. From this point 
eastward, this ancient erosion had made great inroads upon the 
continuity of the Cupriferous and older rocks before the deposi- 
tion of the Silurian sandstone. The melaphyre ridges are broken 
into knobs, or are wanting, and no Huronian was found as far 
as the Ontonagon river, seven miles away, and the limit of our 
observations, 
.E. corner of Sec. 5, about four miles distant. It is a charac- 
clusions we are drawn to are these : 
he Cupriferous series was formed before the tilting of the 
Huronian beds upon which it rests conformably, and conse- 
quently before the elevation of the great Azoic area,* whose 
existence during the Potsdam period pre-determined the Silu- 
nan basins of Michigan and Lake Superior. 
fter the elevation of these rocks, and after they had 
assumed their essential lithological characteristics, came the 
deposition of the sandstone, and its accompanying shales, as 
It Is still uncertain whether they should be referred to the Pots- 
dam, Calciferous or Chazy. e question would still seem to 
n open one, whether the Cupriferous series is not more 
Rearly related in point of time to the Huronian than to the 
Silurian. 
Our observations have detected a lack of conformability 
between the Laurentian and Huronian at several points on the 
pper Peninsula. On the other hand, in the — have 
n discussing, which is the only one where the Huronian and 
Cupriferous are seen in contact, there seems to be a well-marked 
