Lake Superior Iron Ores.—S purr. 349 
Conclusions. 
The writer, therefore, states his conclusions as follows: 
1. That the iron ores of the Mesabi range, and the var- 
ied and peculiar rock-types of the iron-bearing formation 
are derived from the alteration and rearrangement of a sedi- 
mentary rock containing large quantities of a green hydrous 
ferrous silicate, in generally rounded, small, separate grains. 
2. That the rocks containing iron carbonate, including 
‘the phases called cherty siderites and sideritic cherts, are one 
of the results of alteration of this original rock, the iron car- 
bonate and also a large proportion of the silica being derived 
from the green silicate. 
3. That the green silicate was formed largely through 
the agency of organic matter. 
4. That its habit, form, optical and chemical qualities 
mark it as belonging to the class of glauccuites, and mark 
the original rock as a green sand. 
5. That in accordance with what is known of the form- 
ation of green sand, the iron, silica, etce., of which the glau- 
conite is composed, were probably derived largely from fine 
land silt,* in part also from solution in the sea water.+ . 
6. That the above conclusions probably apply to most 
of the other lake Superior iron ores. 
SOME TERTIARY FORMATIONS OF SOUTHERN 
CALIFORNIA. 
By Oscar H. HERSHEY, Berkeley, Calif. 
INTRODUCTION. 
In the course of several short pedestrian .excursions, ag- 
gregating 600 miles, the writer had the rare fortune of en- 
countering in southern California, during this present winter, 
an interesting series of Tertiary formations which had not 
hitherto been reported and discussed; and while the object of 
the excursions was primarily one not purely geological, suffi- 
cient material was gathered, it is believed, to warrant its being 
thus publicly recorded: for every addition to our knowledge 
* Bull. X, Minn. Geol. and Nat. Hist. Surv., p. 240. 
+ Op. cit., p. 243. 
