Concctitratioii by WcatJicring. — Kimball. 159 
The third or upper division is characterized by a sub- 
nietalHc lustre and by prismatic cleavage- — both evidently de- 
veloped by weathering. Although apparently of the same 
mineral composition as the two lower beds, it is in places 
largely made up of pebbly or spherulitic differentiations, the 
origin of which is an interesting object of inquiry thus far 
unaided by the microscope. Interposed between aphanitic 
layers and an overlying siliceous conglomerate, this bed, 
macroscopically at least, has the casual appearance of coarse 
augitic psammite. Between a clastic origin and a concretion- 
ary origin of the spherulitic contents there lies a doubt. These 
have become pronounced, if, indeed, they have not actually 
been developed, by weathering action, as manifested by partial 
or complete replacement of the original material with anhy- 
drous oxides of iron. In comparatively u;:altered rock, as 
on the Monarch location, the only feature in obvious relation 
to such occurrences is a mottled fracture suggestive of unpro- 
nounced or incipient concretionary structure. In some parts 
of this bed, as on the Boss and Iron Monster locations, an 
iron ore of tolerable quality is developed by more or less 
complete conversion of " the spherulites into ferric oxide. 
Isolated and protuberant examples of these products bear 
resemblance to terebratuloid forms. The mineral alteration 
which they have undergone is of the same kind as that which 
has taken place on the surface of exposed ledges and on cleav- 
age surfaces. While it is true that the third bed which, as 
the most pronounced in character must be regarded as the 
physical type of the thin series, is not without features in 
common with a clastic tuff of volcanic origin, the above facts, 
taken along with certain negative evidence, point, as I con- 
clude, to a metamorphic origin. 
Every gradation in tenor of iron oxides from unaltered to 
highly metalliferous material is j^resented by all of the beds — 
sometimes within a very narrow compass. Material from all 
of the beds exhibits polarity. Fragments from the middle 
1)ed on Iron Mt., where the attitude of the series is nearly ver- 
tical, act as powerful loadstones. Even the unaltered greenish 
augitic material, charged with minute grains of magnetite, is 
not without decided effect on the magnetic needle. The pres- 
ence of lime, as shown by analysis, is doubtless an important 
agent in the transformation above described. As in most 
