IRON ORES OF THE CLINTON FORMATION 47 



they are observable only with the aid of the microscope. The kernels 

 sometimes appear to be wholly absent. The quartz has the same 

 character as that found in granitic rocks, showing liquid and gas 

 inclusions, as well as rutile and hematite crystals. Its ultimate 

 source, undoubtedly, is the Precambric crystallines, but the small 

 size of the grains and their well rounded forms indicate long con- 

 tinued abrasion after its release from the rocks. 



The texture of the fossiliferous ore varies to some extent with 

 the locality. In the red flux bed as exposed at Clinton, the fossil 

 fragments are coarse and the different forms can be separated and 

 identified without difficulty. In the w^estern part of the State, the 

 beds show much finer texture, while the shell particles have been 

 worn and smoothed until their organic nature is more or less con- 

 cealed. The smaller fragments are often enveloped by one or more 

 layers of hematite deposited after their replacement in the same 

 way as with the oolitic grains. 



The cementing material in both kinds of ore is usually granular 

 calcite. There is considerable variation in the relative proportion 

 of this mineral to the hematite. Local variations may be ascribed 

 to solution of the calcite after the ores were laid down, but it is 

 also to be expected that the conditions of deposition w'ould change 

 from time to time and from place to place. An exceptional type is 

 represented in the eastern section in Herkimer county where there 

 are one or more layers of what is properly a ferruginous sandstone. 

 The fine quartz grains are not coated with hematite to any extent, 

 but the latter fills the interstices as cement. The material is too 

 lean to be classed as an ore. 



Chemical character 



The Clinton ores show considerable regularity in their chemical 

 composition. Leaving out of consideration the locally occurring 

 beds which are generally too lean or too thin to be workable, the ores 

 throughout the State may be said to average about 40^ in metallic 

 iron. They seldom run above 45^ or less than 35^. The higher 

 limit is approximated by the oolitic bed in the vicinity of Clinton, 

 where the mines of the Franklin Furnace Co. have returned an 

 average of 44;^ through a period of several years. The care taken 

 in separating the ore from the inclosing rock and in the removal of 

 shale, sandstone or limestone partings which arc often jnescnt. is an 

 important factor in determining the yield. According to C. A. Borst, 

 the middle portion of the Clinton oolitic bod can be mined to give 



