METEORITES OF NORTH AMERICA. 473 



quently intersecting one another; usually, however, they occur more sparingly and so widely separated that they but sel- 

 dom intersect. A sharp contrast between the lines is often observed also. Between the etching lines and in the larger 

 spaces free from the latter the nickel iron is unusually rich in closely and regularly distributed pittings. Although 

 these appear to be all of the same character, I consider it possible, judging from the conspicuous abundance of rhabdite 

 in a solution, and the comparatively small number of visible needles of this substance, that they are not exclusively 

 etch-pittings, but that rhabdite, slightly etched and oriented perpendicular to the section surface, contributes to the 

 formation of these depressions. In the immediate vicinity of larger and deeper etching lines, as well as of larger rhab- 

 dites and even at a somewhat greater distance from the schreibersite, the pittings are wanting as a rule, so as to produce 

 a smooth and shiny etching zone — of a maximum breadth of about a millimeter — in which by the aid of a powerful 

 glass still finer etching lines can be discerned, and which show the same oriented luster as the principal mass of the 

 nickel iron. Upon this zone is found by the side of the schreibersite an area of nickel iron which, in sharp contrast to the 

 bright and uniform oriented sheen of the principal mass, appears dull gray and of a dull luster. Where the schreibersite 

 lies isolated and widely separated the two areas — of which the outer is twice as wide as the inner — follow the outline 

 of the schreibersite. Where the schreibersites are nearer together the dull zones become united and form extended 

 and very irregular but sharply-defined dull patches, which give the etching surface a very peculiar appearance. But as 

 large portions of the nickel iron do not have this character, it may be wanting on small specimens of the Walker County 

 iron. These dull gray patches give the impression of fine-grained nickel iron; but as finer etching lines may be dis- 

 cerned within these areas I consider it probable that densely crowded and deepened etch pittings are the cause of the 

 varying appearance of such portions of the etching surface. The rhabdites, mostly 1 mm. long, often shorter, in isolated 

 instances reaching a length of 8 mm. and arranged in two directions perpendicular to each other, are so fine that they 

 can only be distinguished from etching lines by the aid of a high-power microscope. In a certain light they appear, 

 however, as very fine, brightly gleaming streaks. The distribution is so irregular that spaces of 4 sq. cm. in size are 

 entirely free from them, while they are much crowded in some places. Nickel-iron phosphide occurs also in the form 

 of schreibersite, irregularly distributed; it consists of elongated crystals as much as 1 cm. in size with uneven surfaces, 

 which after polishing appear hollowed out under the protection of a small compact border zone. Whether the crystals 

 possess a porous center or are compacted together with troilite and daubr£elite at the central part, which crumbles out 

 by polishing, can not be determined. Troilite in distinctly recognizable inclusions is not to be found on the 100 

 sq. cm. section surface; however, there occur here a few fine lamella; easily mistakable for etching lines and having a 

 different orientation from that of the rhabdite, which I regard as Reichenbach lamella, which were also mentioned by 

 Reichenbach 10 on the London specimen ("scales as thin as parchment and 4 cm. long"). Troilite has been observed 

 on other specimens, however, and an isolated portion proved to be an excellent conductor of electricity. 21 In general, 

 nevertheless, accessory material occurs very sparingly in the Walker County iron, as Reichenbach has already shown. 



Walker County takes on a strong permanent magnetism; Leick determined the specific magnetism to be 0.58 

 absolute units per gram. 



In the course of dissolving a piece of considerable size in much diluted HC1 the following observations were made. 18 

 In the nickel-iron, deep straight rills are gradually formed, apparently because the dissolution proceeded rapidly 

 along the twin lamellae. The rhabdite is, as a rule, between 0.001 and 0.004 mm. thick, but both dimensions were not 

 infrequently exceeded (observed extremes, 0.0009 and 0.03 mm.). The insoluble residue contained chromite and 

 grains of silica. The former consisted of irregular grains and fragments, besides fine octahedrons and dodecahedrons. 

 Among the silicate grains much the most prominent are colorless ones, with low interference colors and mostly high, 

 but occasionally low, indices of refraction. Next in amount come colorless strongly doubly refracting grains, some- 

 times with an index of refraction which approaches very closely that of Canada balsam, sometimes with a wider 

 border. Sparingly occur colorless, six-sided plates resembling tridymite with weak anomalous double refraction — 

 bluish, pleochroitic grains with weak double refraction and distinct but not very broad outline — broken grains. 

 Finally, there remained a lamella of schreibersite 10 mm. long, 2 mm. wide, and about 0.25 mm. thick, whose pres- 

 ence was not noticed before treating the plate with HC1. 



Analysis (Hildebrand): 



Fe Ni Co Cu Cr P S 



94.14 5.30 0.64 0. 0G 0.05 0.28 0.19 =100.66 Sp. gr., 7.7806. 



Composition: 



Nickel-iron 97. 70 



Schreibersite 1. 81 



Daubreelite 0. 14 



Troilite 0. 35 



100. 00 



Walker County has been much confused with Limestone Creek, also with a pseudonieteorite. 

 The history of these errors is given by Cohen, 22 as follows: 



According to a brief communication from Fletcher, the principal mass (65.75 kgs.) of this iron was offered for sale 

 in 1843, under the name Alabama, by Troost, through the medium of Heuland, to the British Museum, which acquired 

 22.5 kgs. It may be assumed with certainty that the remainder of the mass came into the possession of Reichenbach, 

 since he states that the other half of his piece was in London (9.119), and since the two pieces together weigh 62.5 kgs. 



