80 'Jlw A iiierl<-<()i (icohKiisf. August, 1895.. 
l)y sul)sick'nce of the region by which the Animikie and its 
nioclitied beds and associated gabbros, red granites and fel- 
sytes, were covered by the ocean, it is apparent that the great 
eruptions of the period began in the midst of tlie formation of 
a sandstone. The flexures that were the attendants of this 
subsidence and eruption were very great. In some places the 
very rocks themselves which constitute the jn'edominant fea- 
ture of the Keweenawan were broken and violently scattered, 
either by erosive action or by volcanic ejection, probabl}'^ by 
both. The formation of a conglomerate, which Irving reports 
as 1,300 feet thick imbedded in the typical Keweenaw^an on 
Montreal river, was not the event of a year nor of a century. 
Several fragniental beds occur on the north shore of lake Su- 
perior interstratified in the series. How" far they continue as 
independent strata is not known, but it is very probable that 
they have a general parallelism with those found on the south 
shore. The sandstones become conglomeratic. Indeed the 
wide dissemination of coarse material, especially of felsitic 
antl red-porphyritic rock, during the time of the Keweenawan 
is one of the most common features of its fragniental strata. 
It goes, therefore, without saying that the existence of Ke- 
weenawan conglomeratic material is not, per .ve, any proof of 
pre-Keweenawan time, nor evidence of the existence of a great 
erosion-plane of sutHeient significance to warrant the intro- 
duction of an important time interval. Yet it is just such 
evidence as this and an occasional non-conformity which 
forms the basis of the assumption that the sandstones which 
are seen non-conformable on the traps at sundry points are of 
an age widely different from the traps. 
In order to make it clear what value the individual cases 
may have it will be necessary, in the next place, to examine 
the reports which have been published concerning them. 
Some of these descriptions omit important data, perhaps be- 
cause not obtainable. In some cases later examinations have 
supplied these missing data, but in others they are lacking 
still. 
The St. Croix Falls case is perhaps the most frequently re- 
ferred to. Prof. Irving depended on this to establish the 
enormous erosion interval between the traps and the overlying 
sandstone and inferentially to prove such an interval between 
