0. C. Farrington — Analysis of "Iron Shaky 305 



jet to have been published. As it seems desirable to throw as 

 much light as possible on the remarkable character of the 

 formation of Coon Mountain, the writer deemed it advisable 

 to determine what information might be gained from a quanti- 

 tative analysis. Specimens of what seemed to be the same 

 material as that described by Messrs. Barringer and Tilghman 

 were already in the Field Museum collections, But in order to 

 be certain to obtain the material described by them, a request 

 was made of Mr. Barringer for specimens. These Mr. Bar- 

 riuger very kindly furnished, in the shape of several pieces of 

 " shale " weighing in all about half a pound, as well as one of 

 the small " shale balls." The pieces of shale received were of 

 flattened or elongated form, angular, and weighing a few 

 ounces each. All showed a quite uniform blackish-brown 

 color. On fresh fracture the color appears more nearly black, 

 and the surface has a glossy appearance. A laminated struc- 

 ture characterized all the pieces. The laminae of which the 

 shale is made up are more or less intercalated but average 

 about one millimeter in thickness. The divisions between 

 them are made in part by thin layers of a brownish-white sub- 

 stance which effervesces with acid and is undoubtedly the 

 aragonite coating frequently observed on the Canyon Diablo 

 siderites and described by Foote. These layers do not affect 

 the appearance of the shale to the naked eye, however, for 

 without a lens only a uniform color and structure is apparent. 

 The shale is sufficiently coherent also to take a fair polish. 

 The " shale ball " received from Mr. Barringer is in color and 

 texture similar to the shale. Its lamination is however concen- 

 tric rather than horizontal. Fes form is ellipsoidal and diame- 

 ter about one inch. Its surface is broken by broad, irregular 

 cracks extending nearly to the center. Both the shale ball and 

 a piece of the shale showed the same specific gravity, viz : 

 3*73. The large pieces of shale show sufficient magnetism 

 to affect a compass needle, and small pieces are readily 

 attracted by a common horseshoe magnet. The shale crushes 

 rather easily in a mortar to a dark brown powder. This 

 powder is also quite magnetic. Heating in a closed tube 

 causes considerable water to be given off, showing that a 

 hydrous oxide is present. The material appeared, therefore, 

 to be referable neither to magnetite nor to limonite, since it 

 was too magnetic for limonite and contained too much water 

 for magnetite. None of the specimens showed the green 

 hydroxide of nickel referred to by Foote and Barringer. 

 Only the powder which was attracted by the magnet was used 

 for analysis, but this included practically all of it. The 

 analysis by Mr. H. W. Nichols gave the following results : 



