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



He states that "in no case, however, was anything noticed 

 leading to the opinion that concretionary segregation of iron 

 had taken place either around the bryozoan fragments or other- 

 wise." Had Dr. Foerste's observations extended to the two 

 lower beds of ore at Clinton, he would have been led to modify 

 this statement, for in these the concretionary structure is very 

 marked. It is unnecessary to employ the microscope to 

 observe this. If the ore be coarsely broken and the separated 

 spherules placed on a steel plate and tapped lightly with a 

 small hammer, each spherule will break into a series of concen- 

 tric shells, and finally a nucleus will be reached, which is nearly 

 always a rounded fragment of quartz. In thin sections, owing 

 to the opacity of the material, this structure may be easily 

 overlooked, unless the section is ground extremely thin (a dif- 

 ficult matter with this ore), or is examined by reflected, as well 

 as transmitted, light. Thin sections show well the character of 

 the quartz around which the iron is segregated. The fragments 

 are all well rounded, having been subjected to the attrition of 

 the waves along a coast line. Inclusions of liquid and gas are 

 very abundant, besides long needles of rutile and scales of mica- 

 ceous hematite. The derivation of the quartz from granitoid 

 or schistose rocks is evident. 



On treating the spherules with hydrochloric acid the iron is 

 dissolved, and there is left a perfect cast of the spherule in 

 silica, containing a little argillaceous material. This siliceous 

 cast or skeleton of the spherule is, of course, transparent and 

 in it the concentric structure can be seen more perfectly than 

 in thin sections. The number of layers is seen to be large, 

 often ten or more. With polarized light the silica appears 

 sometimes to be amorphous, but usually gives aggregate polari- 

 zation, like that often seen in chalcedony. Thus, the two lower 

 beds of ore at Clinton are truly oolitic, consisting of grains of 

 sand enclosed in concentric shells of intimately associated 

 ferric oxide and silica. 



A sample of the Clinton ore from Dodge County, Wis., 

 kindly furnished by Dr. W. H. Hobbs, gives similar results. 

 This ore is an almost incoherent mass of spherules, associated 

 with rocks quite different from those at Clinton, but the 

 spherules have the same concentric structure, and give the same 

 siliceous skeleton with hydrochloric acid. There is one marked 

 difference, however ; the quartz nucleus is greatly reduced in 

 size in the Wisconsin oolite, or is more often entirely absent. 

 Samples of Clinton ore from Rochester and Ontario, N. Y., 

 Chattanooga, Tenn., Dade County, Ga., and Birmingham, Ala., 

 have been examined, and though none of these are strictly 

 oolitic in appearance, still, the spherules in varying proportion 

 are scattered through them. Moreover, when the ore consists 



