344 The American Geologist. June, 1902. 
exact amount of silica in the silicate (which was taken at 50 
per cent), and from this to compute the proportions of the 
bases. The results of these two analyses are given below, side 
by side with three analyses of undisputed glauconites: 
Glauconite, Glauconite, 
Grodno French Glauconite, Mesabi Mesabi 
Valley, creek, Paris green green 
Russia.* Penna.j+ Basin.i mineral.§ mineral.|} 
Sili@avice.cccsvester-eermes 49.76 52.86 40.00 50.00 50.00 
PACHA Aeeeee se eececemes 8.18 7.08 1.00 5.54 C26 
Sesquioxide of iron 16.80 1,205 N 24.70 8.05 9.81 
Protoxide of iron.. 3.77 OES it) ne 26.56 17.91 
Mapnesia........... ie) ROTO 2.90 16.60 3.78 5.45 
1Dyi01\2inenbee apascaccaa acd 0.41 trace 3.30 2.59 17h 
Potashicsaie dees -asaee TheBsTt 2123 1.70 41 so 
Sod Gisstvesaeserresseesseh- OraZ CHACET, Je yaesscecees 45 trace. 
WAVE WS Pbeacegocadonsonceras 9.82 84.3 12.60 2.54 7.54 
100.00 100.18 100.00 99.92 99.99 
Among these analyses the writer considers that Nos. 2 and 
5, an undisputed glauconite and the Mesabi green mineral, 
are much closer together than 1 and 3, two analyses of glau- 
conite. 
Chemically, therefore, there seems no reason why the Mes- 
abi green silicate cannot be classed as a glauconite. Its iron is 
chiefly in the protoxide state, whereas in most glauconites it 
is chiefly sesquioxide; but the French Creek glauconite quoted 
above contains likewise chiefly protoxide. Dana° speaks of 
the California Cretaceous glauconite as a ferrous silicate (20 
to 25 per cent protoxide of iron). Zirkel’s general definition 
of glauconite, above quoted, gives preference to the protoxide 
over the sesquioxide. In this point, at least, then, there is no 
possible difficulty. 
The final chemical point is the question of the trifling 
amount of potash present. This question was raised and 
discussed by the writer in his original work. 
The most ordinary glauconite contains 6 or 7 per cent of 
potash (the highest under the writer’s observation at present 
is 7.91 per cent), but many analyses show 3 or 4’ per cent only. 
Analysis No. 2, quoted above, contains 2.23 per cent; analysis 
No. 3, 1.70 per cent; while a specimen analyzed by Murray 
* JANA, System of Mineralogy, 6th ed , p. 684. 
+ Ibid. 
+ BERTHIER, Annales des Mines, 6. 1821, p. 459. 
§ Bull. X, Minn. Geol and Nat. Hist. Survey, p. 233. 
\| Op. cit.. p. 235. 
° Manual of Geology, 3d edition, p. 458. 
