248 The American deologist. April, 1396 
from the strata" through which they were intruded. The conglomerate 
at Stuntz island they consider one of the brecciated intrusives of the 
acid scries, and Dot a true conglomerate. 
In some manner the apparently fragments and even bouldery aspect 
of the greenstones, whether at Soudan or at Ely, they attribute to the 
brecciation of an original, massive, basic eruptive. 
The merchantable deposits of the ore they believe to have been formed 
from local causes tending to concentration of iron oxide at favorable 
points. Thus the accidental pose' of a basic eruptive, as it pierced the 
strata, afforded routes of underground drainage along which surface 
waters entered, carrying organic matters. These waters became alka- 
line, removed silica and deposited iron oxide. 
The authors have made an important contribution to the geology of 
an interesting and complicated region. Their conclusions differ from 
those of the Minnesota survey in several important particulars. It may 
be they are correct.^ But there are some difficulties which remain 
which their theory does not fully explain. It is not best here to discuss 
them. It is only necessary to remark that, while we consider their 
contribution a very welcome addition to a progressive investigation, 
the result is not closed. n. h. w. 
British Geology. By T. Mellard Reade. (Geological Magazine, 
decade iv, vol. n. pp. 557-565, 1895.) In his recent presidential address 
to the Liverpool Geological Society Mr. Reade shows briefly the part 
that the geology of the British isles takes in illustrating the origin of 
mountain ranges. In this connection he gives a summary of his latest 
opinions regarding the cause of orographic movements and ascribes it 
entirely to changes of temperature, producing expansion and contrac- 
tion, and not to the shrinkage of the nucleus of the earth, the closing in 
of the non-shrinking crust upon it and the consequent folding by tan 
gential pressure. In concluding he says that "Neither does the princi- 
ple of isostacy so insisted upon by American geologists explain the com- 
pression, folding and building up of great masses of sediment into 
mountain ranges. On the principle of isostacy, it must be obvious to 
anyone possessing even a rudimentary acquaintance with mechanics 
that the sinking of the bed of the seas on which great deposits are ac- 
cumulating, and to some extent a rise of surrounding land, may be ex- 
plained, but not the lateral compression and elevation of the sediments 
themselves into mountain ranges. 
"Where, then, are we to look for the agency constantly associated 
with the deposit of great volumes of sediment which is capable of event- 
ually upheaving them from below the sea level, and by lateral compres- 
sion and folding throwing them into mountain chains? 
"Again, when after the lapse of lengthened periods of geological time, 
denudation has cut away and removed into the sea large masses of ele- 
vated land, what agency is it that causes it to shrink and become trav- 
ersed by great lines of faulting? 
