COMPARISON OF IRON SPRINGS ORES WITH OTHER ORES. V)5 
ore, has been leached by weathering. It must be remembered, 
however, that no one of these deposits has been opened up sufficiently 
to demonstrate their character in depth. 
The theory that iron ores at the contacts of igneous rocks and lime- 
stone have developed entirely by the action of meteoric waters from 
above, leaching ores from the adjacent rocks, has not been without 
supporters. This is the view held by Hill for the Durango deposit. 
The senior author presented this theory as possibly applicable to the 
Iron Springs deposits of Utah in an earlier publication. It would be 
entirely premature to exclude this hypothesis for all iron ores in 
fissure veins in igneous rocks or along their contacts with limestone, 
especially where these ores are largely limonite and apparently lack 
heavy anhydrous minerals, as in some of the deposits of northeastern 
Washington. It is usually where the ores are hard crystalline magnet- 
ites and hematites, intimately associated with the anhydrous sili- 
cates and adjacent to or within igneous rocks, that there is reason- 
able probability that the origin of the ores may be ascribed to the hot 
solutions coining from the igneous rocks. 
STRUCTURAL, DISSIMILARITIES OF THE IR(W SPRINGS 
DEPOSITS TO OTHER CLASSES OF IRON-ORE DEPOSITS. 
The structural features in which the iron-ore deposits of the Iron 
Springs district differ from ores of sedimentary origin, like the Lake 
Superior and Clinton ores, are obvious to all familiar with the great 
classes of iron-ore deposits, but for those who are not so familiar an 
elementary comparison may be of interest. 
The Clinton hematites of Alabama and elsewhere are bedded 
deposits with all the stratigraphic and structural characteristics of 
sedimentary rocks. Given a bed, it may be expected to extend in 
strike and dip, thicken and thin, with about the same degree of uni- 
formity as may be observed in other sedimentary layers, such as 
limestone or shale adjacent. Its structure also, as shown by strike 
and dip, is governed by the same laws as other deformed beds. It is 
thus frequently possible to determine with some certainty extensions 
of deposits for many thousands of feet. The Iron Springs deposits 
can not be followed or extensions calculated with any such certainty. 
The Lake Superior iron-ore deposits are more or less irregular con- 
centrations in a sedimentary "iron formation." The iron ores make 
up a very small per cent — less than 2 — of the mass of the iron for- 
mation. The iron formation originally consisted of iron carbonate or 
iron silicate, and was altered to iron ore, ferruginous chert, or jaspilite, 
but retained its bedding. The structure and stratigraphy of the iron 
formation may be worked out as fully as for limestone or quartzite. 
Exploration is limited to the iron formation, and the presence of an 
