342 The American Geologist. June, 1902. 
potash, and so cannot be glauconite and of organic origin* 
as supposed by Spurr.’”’+ 
This is hardly sufficiently tangible. The statement that the 
mineral is a ferrous silicate, and the observation concerning 
the absence of the alkalies, potash and soda, reiterate those of 
the present writer. The reader will doubtless be puzzled to 
know, as much as is the author of this article, why the same 
characteristics, which the author considered compatible with 
the consideration of the mineral as glauconite, should now be 
stated as full proof to. the contrary. 
The last sentence quoted above may be resolved into two 
statements—First: “They lack potash and so cannot be glau- 
conite”’; and second, “They lack potash, and so cannot be ot 
organic origin.” The first statement admits of a discussion; 
but the logic of the second does not appear. It is probable, 
however, that this last is a hasty statement, and was hardly 
meant, for in the next paragraph, after speaking of the evi- 
dence of sedimentary origin of the iron-bearing formation, 
and advancing the hypothesis that the iron was precipitated 
from the sea-water as limonite, the author of the report goes 
on to say: 
“The limonite settled and became mingled with organic 
material, the presence of which is shown by the association 
with carbonaceous slates, and was reduced to the protoxide 
form. The simultaneous decomposition of the organic ma- 
terial freed carbon dioxide. Silica also precipitated (chert is 
known to develop under such conditions) probably through 
the agency of organisms. Both of these substances could com- 
bine readily with the iron protoxide, but im the case of the 
Mesabi rocks the main combination was the protoxide and sil- 
ica, = giving the ferrous silicate which we now find.” 
Therefore, after all, the author assigns an organic origin to 
the ferrous silicate, and the question may be dropped. Briefly, 
he believes that iron protoxide reduced to this form by organic 
material, and silica precipitated by the same agency, united 
“to form the hydrous ferrous silicate. This is exactly the 
theory which is generally held, and which the present writer 
holds, concerning the origin of glauconite. 
* The italics are mine. (J E.S.) 
+ Report of paper before the Geological Society of Washington, by C. Kk. 
LEITH. in Eng. and Min. Jour., Feb. 22, 1902, p. 277. 
t{ The italics are mine. (J. E. 8S.) 
~~. = 
