. The prospector's field-book and guide in the search for and the easy determination of ores and other useful minerals. Geological Horizons around the Iron Ores op Lake Gneiss, b, Hornblende slates, c. The same with numerous thin bedsof iron ore which frequently unite, d. Potsdam sandstone. beds and deposits; they are on the lower levelswhen they were formed, although in after ages theymay have been uplifted. Iron ores are, therefore, to be found in three gen-eral geologic regions: (1) in the earliest rocks; (2)in the carboniferous, and (3) in the more recent orsedimentary rocks, a
. The prospector's field-book and guide in the search for and the easy determination of ores and other useful minerals. Geological Horizons around the Iron Ores op Lake Gneiss, b, Hornblende slates, c. The same with numerous thin bedsof iron ore which frequently unite, d. Potsdam sandstone. beds and deposits; they are on the lower levelswhen they were formed, although in after ages theymay have been uplifted. Iron ores are, therefore, to be found in three gen-eral geologic regions: (1) in the earliest rocks; (2)in the carboniferous, and (3) in the more recent orsedimentary rocks, and in accordance with their 198 PROSPECTOR S FIELD-BOOK AND GUIDE. composition as magnetites and specular ores, ascarbonaceous or black band and spathic ores, or asbrown ores of the limonite order. One of the most peculiar geologic conditions is <*W North 1) a Section of Pilot Knob, Quartzite or siliceous rock. b. Red hematite iron ore alternating withsiliceous matter, c. Siliceous rocks. found in the Pilot Knob Mountain, wherein theiron strata have been thrown up as in Fig. 59. THE USE OF THE MAGNETIC NEEDLE IN PROSPECTINGFOR IRON. In ordinary cases, where the surface is coveredwith loose earth, it is common to search for mag-netic iron ore with a magnetic needle or a minerscompass, and for preliminary examinations it isnow the chief reliance. In using this instrumentconsiderable practice is required ; but this joined togood judgment gives indications of the presence ofore which are almost infallible. There has beenvery great improvement, within a few years past, in ZINC AND IRON. 199 the methods of searching for magnetic ore as wellas in the instruments to be used for that purpose,and the work is now well done by many persons. In the Annual Keport of the State Geologist ofNew Jersey for 1879, W. H. Scranton,
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