2o Field Columbian Museum — Geology, Vol. i. 



Upon close examination the bands are found to be made up of a 

 broad, central plate depressed below the surface, which is bounded by 

 narrow ones in relief. These are shown in Figs, i and 2, Plate II. 



Analysis of these plates by Reichenbach has shown that the 

 broader ones are made up of an alloy of nickel and iron containing a 

 large percentage of iron and hence readily dissolved by the acid. 

 This alloy he called kamacite. The narrow plates, made up of an 

 alloy which he called tacnite, contain a larger percentage of nickel, 

 are less readily dissolved and hence stand out in relief. The ground 

 mass, to which he gave the name of plessite, he considered as having 

 a proportion of iron and nickel between the two. Recent investiga- 

 tions by Davison,* however, indicate that there may be but two alloys 

 present, the plessite representing simply portions of the mass where 

 the bands of taenite are so closely crowded as to protect the kama- 

 cite from the action of the acid. This is rendered more probable 

 by observing the insensible gradations by which the finer lines, 

 called by J. L. Smith Laphamite markings, pass into the ground 

 mass as if there were no real division between them. See Plate II, 

 Fig. 1. 



The angles at which the bands meet are dependent, as has been 

 stated, upon the direction of the section and also upon their parallel- 

 ism to the faces of either the octahedron, cube or dodecahedron, of 

 the isometric system. All of these planes may occur in one meteorite 

 but commonly only those of one kind appear and give to the iron a 

 characteristic structure, distinguishing them as either octahedral or 

 cubic. 



The varying thickness of the plates and differences in their 

 angles of intersection produce a variety of figures which characterize 

 irons of different falls. See Plates I, II and III. Since they were 

 first described by Widmanstatten, they are called Widmanstatten 

 figures. They form one of the most striking features of the metallic 

 meteorites and were long thought to be peculiar to such bodies, but 

 are now known to be imitated by the etching figures of steel and of 

 the native iron of Greenland. They have been produced by Daubree 

 upon a mass artificially formed by fusing together iron, nickel and 

 phosphides of iron and nickel. They are, therefore, rather to be con- 

 sidered as indicative of the conditions under which the meteoric mass 

 originated than as representing any distinct property of extra-ter- 

 restrial matter. 



As examples of coarse etching figures, i. e. those made up of 

 broad bands, may be noted sections of the Toluca (16), Staunton (79), 

 Robertson Co. (83) and Canon Diablo (147), irons. More delicate fig- 



*Am. J. Sc 3rd ser , Vol. 42, p 64. 



