A jRah'o/ifif }"ieir of the Keireeitd ii'dii. — WlnchelJ. 151 
ments that the sandstones are broken and thrust in various 
attitudes in their immediate relations with the traps. 
8. The shortest observed interval between the horizontal 
sandstones and the tilted sandstones, within which such non- 
conformity must occur, if it exist at all, is four miles, viz., 
between Montreal river and Clinton point, both in Wisconsin. 
9. If it were to be affirmed that there is no such non-con- 
formable contact between these sandstones, the statement 
could not be disproved b}' any known facts. 
10. If the statement were to be made that the upper part of 
the Keweenawan sandstones passes conformably into the hori- 
zontal, as represented in figure 1, in all places where thej'' are 
in contact, excepting only a slow subsidence of the whole re- 
gion, bringing the later horizontal sandstones unconformably 
over wider and wider areas of formerly tilted rocks, such 
statement could not be disproved by any known facts, but 
would be in harmony with all that is known of these forma- 
tions. 
Kontreal River 
Cliatsn Pbint' _^-rrf77W77fMMW- 
Figure 1. Structural relations of the sandstones at Clinton point, Montreal river 
and Silver creek. This collocation of tliese outcrops is warranted by Prof. Irving's 
final mapping of the sandstones on Silver creek, in Ashland, Co., Wis. (Copper-bear- 
ing Kocks, plate xxii. ) 
Up to the date of Maj. Brooks' work in the Lake Su])erior 
region it had generally been considered that the trap rocks of 
the copper-bearing series, and the sandstones with which they 
are associated, whether interstratified or otherwise, consti- 
tuted essentially^ one formation, all the non-conformities that 
were observed being local phenomena such as an epoch of 
eruptive disturbance would be subject to. When, however, 
the non-conformable underlying trap rocks at Taylor's Falls 
(i. e. St. Croix falls) were traced from that point to tlieir 
connection with the trap rocks in the northern part of Wis- 
consin and Michigan, it was thought at once that the evidence 
bore out the conclusion that the upper sandstoiu- was a for- 
mation distinct from the copper-bearing series. The upper 
sandstone being considered, at Taylor's Falls, as of Potsdam 
age, it was appropriate, with that view of the evidence, to give 
a new name to the trap rocks. When later it was found that 
a great thickness of sandstone is sometimes seen tilted con- 
