Decoviposition ({f Iron Py riles J 43 



surface examined, but mostly comprised tlie following points of 

 structure in the pyrite itself : 



First. A coarse columnar structure, that of the fibration, 

 presenting a width of about 0.08 to 0.25 mm. between the par- 

 allel fissures, whose lips were about 0.005 mm. apart. This was 

 crossed, with more or less irregularity, by fissures at right an- 

 gles, often producing the effect of an imperfect tesselated pave- 

 ment or of rude masonry. In places the disintegration had 

 gone so far that the mass consisted of dark roughened needles 

 attached only at one end or both. 



Secondly. The surface intervening between these cracks was 

 ])itted with cavities of the utmost irregularity of size and form, 

 though commonly approximating 0.004 to 0.009 mm. in diam- 

 eter, scattered in rows and in large groups. As a result of the 

 sub-division produced by these cracks and pits, I estimated that 

 the greater part of the mass was separated into little grains, ap- 

 l)roximately cubical in form and about 0.01 mm. on a side. It 

 would require about a thousand millions of such little grains to 

 make up a cubic centimeter of the material, and the surfaces of 

 these would present a superficial area about ten million times 

 that of the superficies of a solid cubic centimeter. 



Thirdly. The surface between the little pits further showed 

 a very delicate striation, apparently by fine cracks or by minute 

 ribs and furrows, all parallel to the line of fibration but slightly 

 wavy. On an average about 555 of such lines occupied the dis- 

 tance of one millimeter across the fibration, i. e., they were about 

 0.0018 mm. apart. They projected very slightly above the in- 

 tervening furrows and conveyed the impression that they were 

 lines of accretion, running in the direction of the general fibra- 

 tion and originally producing that structure ; that they repre- 

 sented the edges of thin films of a compact matei-ial, flattened 

 out by intense lateral pressure, whose irregularity had produced 

 the wavy disturbance of their lines ; also that their material was 

 harder and perhaps brighter than that in the intervening fur- 

 rows, and that their projection above the surface was but a part 

 of the general erosion, caused by their greater resistance to de- 

 composition than that offered by the intervening films. 



Fourthly. The suspicion of the want of homogeneity of the 

 material was fostered by the occasional distribution, over the 



