C H. Smyth, Jr. — Clinton Iron Ore. 491 



ruginous sandstone, differing from the richer ore in that the 

 grains of sand which form the nuclei of the spherules are 

 much coarser, and the deposit of iron around them corre- 

 spondingly thinner. The difference in the richness of the 

 ores is not, then, dependent chiefly upon a greater or less 

 amount of water action, but is inherent in the two layers as 

 deposited. 



Associated with the ores are many irregular patches and 

 layers, both calcareous and argillaceous, containing a varying 

 proportion of spherules. Though the rock may not contain 

 ten per cent of iron, still the spherules are just as ferruginous 

 as in the purer ore. If they resulted from replacement, they 

 would, naturally be only partially changed. If thin sections 

 be prepared from these specimens, it is seen that the spherules 

 are identical with those of the ore, though completely sur- 

 rounded by pure calcite. How is it possible for an iron bear- 

 ing solution to pass through this compact calcite until the 

 spherule is reached, and then begin to deposit the iron and 

 replace the calcite % It is not uncommon to see spherules of 

 which the outer layers have partially separated from the core, 

 the space thus formed being filled in by the clear calcite 

 cement. 



Such occurrences as these can be explained only by the 

 supposition that the spherules were ferruginous when incorpo- 

 rated into the rock. In samples of this character, iron oxide 

 is also present in the form of flakes or scales scattered through 

 the cement. These scales have sharply defined borders and do 

 not pass gradually into the calcite. If the rock were igneous, 

 the iron oxide would, without doubt, be considered an older 

 constituent than the enclosing calcite, and there seems to be no 

 reason for thinking that this is not equally true in the sedi- 

 mentary rock. Let the proportion of oolites and scales of 

 iron oxide be increased in these hard layers, or, let the calca- 

 reous cement be dissolved out by meteoric waters, and the 

 result will be an ore precisely like the two oolitic beds. 



The foregoing facts have led the writer to the conclusion 

 that the oolitic ores at Clinton are not of secondary origin, 

 but were deposited as hydrated peroxide of iron in the shoal 

 waters of wholly, or partially enclosed basins along the coast 

 of the Silurian sea. The intimate association of silica with 

 the iron of the spherules seems to indicate that they were 

 deposited together. Doubtless a greater or less amount of the 

 iron was in suspension rather than in solution, and it seems 

 possible that even in this condition it would take the oolitic 

 form, being cemented in the layers of silica. Plausibility is 

 lent to this idea by the fact that the silica is usually more or 

 less stained by grains of argillaceous material ; and occasional 



