
ORE-FORMATIONS 235 
In Dunderlandstal, for example, they occur in numerous beds 
(sometimes as many as 500), rapidly interstratified with mica-schist, 
and closely associated with massive beds of crystalline limestone and 
dolomite, from which, however, they are always separated by a variable 
thickness (1 to 10 metres) of mica-schist (Fig. 84). This ore belt has 
been followed continuously for a distance of several miles. It varies 
much in width, sometimes showing a thickness of 30 to 60 metres, and even 
exceptionally 75 to 100 metres, but more usually ranging between 3 to Io 
metres. The ore is a fine-grained mixture of specular iron, magnetite, 
and quartz, with various silicates—the proportion of specular iron being 
double that of magnetite. Usually the iron-ore is scaly, and has the 
character of an iron-mica-schist. The minerals associated with this ore 
are chiefly epidote, garnet, and hornblende, also a little mica, felspar, 
etc., together with scattered microscopic granules of calcite. It may be 
added that the ore contains small percentages of manganese and 
phosphoric acid (=about 1 per cent. apatite). According to Professor 
Vogt, these remarkable ore-beds are undoubtedly interstratified with the 

<__72 metres fe) 
Fic. 84.—SECTION ACROSS ORE-BEARING SCHISTS, URTVAND IN DUNDER- 
LANDSTAL, N. Norway. (After J. H. L. Vogt.) 
S, schists; L, limestone; O, bands of iron-ore with intervening schists. 
schists, and occupy a definite geological horizon in the series. Through- 
out their whole extent they have a similar chemical and mineralogical 
constitution. They have no genetic connection with plutonic intrusive 
masses—the schists among which they occur are the result of regional, 
not of thermal or contact, metamorphism. The mica-schists are obviously 
metamorphosed sedimentary rocks—clay-slates or shales; the ores, on 
the other hand, which are always sharply marked off from the schists, 
could not have been originally mechanical sediments of quartz-sand and 
magnetite-specular-iron-sand, seeing that they contain a somewhat 
constant and relatively high percentage of phosphoric acid. Professor 
Vogt has no doubt, therefore, that the ores were originally chemical 
precipitates, probably formed much in the same way as the iron-ores now 
accumulating in many lakes and bogs. This explanation is in keeping 
with the frequent occurrence of petroleum, mineral pitch, and anthracite 
in the schistose rocks with which such ore-beds are associated. Further, 
the lenticular form assumed by many of the ore-formations is possibly 
suggestive of their deposition in lacustrine hollows. The frequent 
occurrence of phosphoric acid and manganese in the ores are, according 
to Vogt, readily accounted for. Just as the iron must have been derived 
from the breaking-up of iron-rich minerals (augite, hornblende, etc.), so 
