EARLE, INTERBEDDED IRON ORE DEP08IT8 139 



In the first place, any leakage, even though very slow, would promote 

 circulation in the inclosed waters ; artesian conditions depend upon rela- 

 tive, rather than absolute, imperviousness. 



In the second place, differences in temperature would cause the estab- 

 lishment of currents involving a more or less constant circulation. That 

 such differences of temperature do exist between the surface waters at 

 the outcrop of the porous layers and the waters confined at considerable 

 depths is hardly open to question. The density of cooler water is greater 

 than of water at higher temperatures, and therefore such water would be 

 acted upon by gravity, causing the denser water to sink while the less 

 dense would rise. 



In the third place, dissolved salts would add to density of the waters, 

 and if solutions heavily charged with iron salts were admitted to the 

 artesian runways, they would tend to sink until by precipitation they 

 lost a part or most of their load, after which they would tend to rise and 

 give place to other charged water from above. 



Fourth, waters charged with insoluble mechanical sediment would 

 tend to sink and set up circulation within the runway. 



Fifth, oscillating movements of the water would occur because of tidal 

 variations in load, accession of fresh surface water, crustal movements 

 and other minor causes effecting changes of pressure transmitted in 

 various ways, such as through the overlying impervious layer or through 

 the water in the reservoir. 



Slowly moving waters thus act as carriers of iron salts and other min- 

 erals and gases and precipitate much more readily because of relative 

 confinement and slow method of circulation. 



Typical Sections of Clinton Ores 



missouri 



Holt Coimty. Drill hole. Red oolitic hematite of Clinton age, 1,885 

 feet below surface, showed the following section (Crane, 66) : 



Feet Inches 



Purple shales (impervious) 21 3 



Oolitic hematite (porous) 3 8 



Earthy argillaceous hematite 5 



Light green sandy shale (impervious) 2 6 



Bluish green shale (impervious) 64 9 



ALABAMA 



In the Birmingham District, out of about 80 sections extending over 

 forty-two properties, seventy-two included ore seams either fossil or 



