188 REVIEWS 
The theory of origin as outlined in this work is the most complete 
exposition of the subject yet presented and it would be unreasonable to 
doubt, in the presence of the facts presented, the probability of the 
origin of a great deal of iron by its direct extraction from the igneous 
rocks in the manner above stated. The description of the possible 
origin of the banding in the jaspers is without doubt the best solution 
of the problem yet offered, as this feature of the deposits has always 
been a very difficult one to explain by any other theory. However, 
while it is not the purpose of this review to offer a better theory for the 
origin of these deposits, it might be remarked that while the authors 
have been fair and impartial in the presentation of this theory, which 
is largely new but still embodying some of the principles of one of H. N. 
Winchell’s earlier hypotheses, there are a number of arguments which 
will not be accepted by those who hold that the weathering of rocks is 
the most important feature in the development of these deposits. It 
may be felt that sufficient importance has not been attached to the 
influence of physiographic conditions during the weathering processes, 
because bog deposits are developed under special topographic conditions, 
and the fact that so little iron was deposited in the Lower Huronian 
might be explained by the fact that during the early part of the epoch 
the relief was great and coarse clastic sediment was being deposited 
rapidly at the expense of the finer chemical sediments. Could not the 
fact that the percentage of iron in the iron formation is so large, com- 
pared with the amount of the clastics, be explained by selective trans- 
portation by which the chemical sediments were carried to lower ground 
and the clastics left to a greater degree on the higher levels? In the 
folding which followed the lower would be folded down and preserved 
in the synclines. Nor is the possible source of iron in the Huronian by 
the destruction of Keewatin iron deposits given sufficient prominence, 
as the amount of these rocks destroyed must have been very great. 
While there is comparatively little clastic sediment in the Keewatin of 
the Vermilion range there is much feldspathic, poorly assorted material 
in many other areas of iron-formation, which the authors regard as 
Keewatin, and which are in all other respects very similar to the Ver- 
milion area. As to the question why there is not much iron in the great 
sedimentary series of the Paleozoic, which have been produced under 
normal weathering conditions, it may be replied that there are large 
deposits, without associated igneous rocks, in the Clinton series and 
Pennsylvanian system, both of which followed a period of extensive 
deposition of clastics, which represented probably subaerial conditions 
