152 The Ailierirdn (ieoJogist. Soptember, 1895 
i'ormably with the traps, and must thei-efore belong with them, 
it became necessary to divide the sandstone between the Pots- 
dam age and the age of the Keweenawan. When, still later, 
it was found that the overlying strata at Taylor's Falls are 
not of the age of the sandstones which, in the Lake Superior 
basin proper, overlie unconformably the trap rocks, but are 
considerably higher, and actually consist, in part, of the mag- 
nesian limestones which are well known as parts of the Cal- 
ciferous of New York state, it became apparent that the basal 
beds of the supposed non-conformable upper sandstones had 
nowhere been seen, but that the Taylor's Falls locality could 
not be taken to show a wide-spread non-conformity between 
two separate formations, but rather implied that after the 
time of the eruptives there had been, in the Lake Superior re- 
gion, a subsidence which at first brought some of the lower 
sandstones vipon the tilted traps non-conformably, and at a 
later date also brought some of the higher sandstones and 
some of the magnesian limiestones non-conformably upon the 
same beds in other places. These facts, have been brought to 
light since the new name was applied, and they should be 
given their proper significance, since they disturb the grand 
conclusion as to the distinctness of the eruptive age from the 
Potsdam. Without the knowledge of this progressive sub- 
mergence after the epoch of eruption, and without the knowl- 
edge of the later crustal movements which, after the deposi- 
tion of the horizontal sandstones, have disturbed them on a 
grand scale in Douglass Co., Wisconsin, and along the Ke- 
weenaw peninsula, it was a y^xj reasonable conclusion that 
the Keweenawan in all its parts is non-conformable below all 
the "horizontal sandstones." That would be the first inter- 
pretation that would be put upon the facts as seen by Brooks 
and Irving. It seems now, however, that the violent tilting 
and shattering which the Keweenawan strata have suffered 
may in part be of a date as late as after the horizontal 
sandstones, and in part due to local volcanic or other dynamic 
disturbance during the progress of the eruptive epoch, and, 
finally, in part due to a grand crustal movement which has ad- 
vanced since Archean time tending to give both these and all 
earlier strata a synclinal dip toward lake Superior. 
The only point, however, which it is intended to insist on, at 
this place, is the lack of sufficient evidence to show a general 
