Editorial Comtnent. 57 
lapping which brings different beds into contact at different places. 
2. The "joint clay," inchided in the contact phenomena, 
embracing some trap and some sandstone debris, can easily be 
explained by referring it to other source than that of faulting. 
There would be nothing more lilcely than that, in case of an over- 
flow of molten rock on sedimentary rocks, with a subsequent 
tilting of both, there would be, in places, a more rapid decay at 
the contact plane, owing to the mechanical mingling and conse- 
quent difference of grain and texture of the fragments that were 
caught between the two rocks. This progressive decay will not 
only account for the confused "clay," but also for the non-dif- 
ferentiated face of the two formations along tlie contact as de- 
scribed by the authors. 
3. The authors assume that the "trap rock," where it is 
found in the south range, and at Taylor's Falls in the St. Croix 
valley, is of the same age as that seen on Keweenaw point. This 
is a weak point in their argument, for it is not only not proven, 
but it is, in oiu" opinion, open to serious doubt. There is much 
reason to regard the Taylor's Falls trap of a much earlier date 
than that of the copper-bearing rocks on Keweenaw point. 
4. The authors assume that the horizontal sandstones that 
lie unconformably on, or run over or below the Keweenaw trap, 
whether found on Keweenaw point or in the St. Croix valley, 
are everywhere of the same age. This is notonlv questionable, 
but it is demonstrably incorrect. Two different sandstones are 
here confounded — sandstones which have been distinguished be- 
fore by both of the authors as separate and distinct. 
2. The strained interpi'etation of the facts, given 1iv the 
authors, throws a shadaw over the cre(h])ihty of their results. 
When it is remembered that this explanation was adopted by 
them several years ago, before the adverse facts which Dr. 
Wadsworth announced were known, and that thev have written 
extensively, on this hypothesis, the shadow is dee^oened, and there 
remains in the mind of the scrutinizing reader, a suspicion that 
the autliors are not disinterested and perhaps not impartial judges 
of the facts. This is sa\'ing nothing more than might be said of 
any geologist. 
6. The question is open still, and wider open than e\er he- 
fore, as to the a^^c of the copper-bearing rocks of lake Superior. 
