: 
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R. D. Irving—Divisibility of the Archean. 239 
Next north again of this succession of layers, we find, follow- 
ing them, in what appears at first sight to be a conformable 
manner, the alternating sandstones and eruptives of the Ke- 
weenaw series. A closer inspection, however, shows that this 
apparent conformity is apparent only, consisting merely in an 
approximate general parallelism of the layers, which does not 
indicate that the one set of rocks has been succeeded by the 
other without interval of time; for, as we follow the junction 
line of the two terranes eastward or westward, we find the over- 
lying formation in contact, now with the highest layers of the 
under one, again with its middle layers, and again with mem- 
bers near its base. Evidently such a relation can find only one 
explanation; the lower formation has been raised above the sea 
and subjected to a long continued erosion before the deposition 
upon it of the higher one. The accompanying diagram wi 
make this relation and explanation so obvious that further 
description will be unnecessary. 
€ same diagram will also certainly suggest at a glance 
that this upper unconformity is not the only one in the region. 
€ very striking manner in which the southern limit of the 
regularly arranged succession of belts of the slaty formation is 
for med, to the southward, now by granite, again by gneiss, and 
and this argument, it seems to me, there is no evading—the 
Slates contain abundant fragments derived from the more 
