REVIEWS 187 
topographical and structural conditions although a smaller portion may 
have been laid down originally with practically the present: content of 
iron. The materials forming the schist, iron carbonate, and silicate are 
supposed to have been derived principally from basic igneous rocks 
either as magmatic solutions poured into the sea or from solutions of 
iron salts in sea water formed by the action of hot igneous rocks coming 
in contact with the salt water. Some of the iron was derived from 
these basic rocks by weathering and transported to delta deposits while 
other portions were deposited in bogs and lagoons through the action 
-of plant life as bog ore is deposited at the present time. This bog and 
lagoon origin is assigned to the lenses of carbonate in carbonaceous 
slates and shales which appear to be delta deposits but the conclusions 
of Weidman that the Baraboo and much of the Lake Superior deposits 
are of this origin are not accepted. A pegmatitic origin is suggested for 
a portion of the iron and silica and some good evidence is presented from 
the Vermilion district in support of this view. A great deal of evidence 
is also presented to show that the ellipsoidal character of the green- 
stones is due to extrusion under water but on account of conflicting 
evidence, which has been impartially presented, it is felt that the case 
has not been made definite. It is argued further from the results of a 
large amount of data collected that ordinary weathering conditions 
could not produce such great deposits of chemical sediments without 
more clastic materials because there is not sufficient iron in the surface 
rocks nor adequate agencies to transport the iron to the site of deposi- 
tion. These arguments are supported by a set of laboratory experiments 
which show that the very conditions postulated for the field can be 
produced in the chemical laboratory. 
In these experiments it was shown that if hot Keewatin basalt be 
sprayed with salt water, a water-glass glaze is formed and if this water- 
glass be neutralized by hydrochloric acid, silicic acid and sodium chloride 
are produced. If the solution then be boiled it becomes alkaline. Thus 
is demonstrated a source for the alkaline silicates and when ferrous 
chloride and sodium silicate react, iron silicate (greenalite) and sodium 
chloride are formed. If iron silicate be attacked by carbon dioxide 
there is produced iron carbonate and silica. Further, if silicic acid be 
boiled with iron carbonate, greenalite is formed. These and many other 
experiments demonstrate the possible source of the material for the 
building up of the greenalite, siderite, and cherty deposits. Of particu- 
lar interest is the statement that the precipitates of these substances 
show a distinct tendency toward banding. 
