492 C. II. Smyth, Jr.— Clinton Iron Ore. 



masses of oolite are seen, made up wholly of such material, 

 cemented by silica, and yet with the concentric structure just 

 as perfect as in the iron oolite. This would seem to indicate 

 that it is only necessary to have the silica in solution, in order 

 to form oolites. That the silica has not been substituted for 

 calcite by the action of circulating waters, is indicated by the 

 fact that the spherules are inclosed in calcite showing no sign 

 of alteration.* 



The formation of oolitic iron ores under conditions some- 

 what similar to those of the Clinton shore is going on in 

 many places at the present time,f and these ores have but to 

 be dehydrated to resemble closely the Clinton ores. There 

 seems to be no doubt that dehydration takes place slowly at 

 ordinary temperature,^: but even if this be not so, the Clinton 

 ores may easily -have been subjected to the comparatively 

 slight rise of temperature necessary for rapid dehydration. 



Some years ago Professor EL S. Williams called the writer's 

 attention to a thin layer of oolitic iron ore in Cuba, Alle- 

 gany Co., IN. Y., which is of especial interest in this connection. 

 The ore forms a very thin bed, perhaps an inch or two in 

 thickness, and often entirely wanting, in a series of arenaceous 

 and argillaceous shales of Devonian age. The rocks are of 

 shallow water origin, as stated by Professor Williams,§ and 

 there is not the slightest evidence that the ore was ever an 

 oolitic limestone. In fact, the character of the ore and of the 

 associated rocks plainly indicates that the conditions under 

 which they were formed were most unfavorable for the pro- 

 duction of limestone of any kind. The ore was undoubtedly 

 deposited in its present form. This ore differs from the Clin- 

 ton only in the smaller size of the spherules. The quartz 

 nucleus is not relatively so large and is sometimes absent, but 

 there is the same perfection of concentric structure, and the 

 same silica skeleton left by hydrochloric acid. That the two 

 widely separated ores were formed in the same way seems cer- 

 tain ; that they are not derived from preexisting limestone 

 seems, to the writer, almost equally certain. 



Thus far the discussion has been limited to the oolitic ores, 

 as these, perhaps, present the greatest difficulties in the way of 

 accepting the replacement theory. But much that has been 

 said of them applies with equal force to the non-oolitic varieties. 



* See E. H. Barbour and J. Torrey, Jr. : Notes on Microscopic Structure of 

 Oolite with Analyses; this Journal, III, si, p. 246. 



f J. S. Newberry : The Genesis of the Ores of Iron : School of Mines Quar- 

 terly, November. 1880. 



\ " r . 0. Crosby: On the Contrast in Color of the Soils of High and Low 

 Latitudes. American Geologist, viii, p. 72. 



§ H. S. Williams: On the Fossil Faunas of the Upper Devonian, the Genesee 

 Section, New York: Bulletin 41, U. S. Geological Survey. 



