486 PROCEEDINGS OP THE AMERICAN ACADEMY 



which he calls the Trias ; while others of the figures are almost 

 microscopic markings, in which distinct plates of kamacite and plessite 

 cannot be made out even under the microscope. Between these two 

 extremes there is every gradation. The Butler meteorite has always 

 been classed among the octahedral irons. We come next to the 

 Coahuila, which has been classed with the so-called cubic irons. 



A large section of this iron, on being etched, showed innumerable 

 fine lines, seeming at first sight as irregular as the markings on a 

 chopping-block. When this section was examined under the micro- 

 scope, it showed all the characters of the Butler figures, only a degree 

 finer. On studying the directions of the lines, they ajDpeared to make 

 every possible angle with each other, but with a prevalence of right 

 angles. The meteorite is very compact, with 

 usually no external crystalline form, but it was 

 found that on one specimen, by quick blows of 

 the hammer, cleavage masses could be broken 

 away. One of these cleavage masses is shown, 

 of twice its original size, in Fig. 5. It has 

 the well-known form of the cube twin, described 

 by Tschermak * as typical of the Hauptmanus- 

 dorf iron, but with this difference, that the cube 

 in this case is modified by the octahedron. On 

 polishing and etching the crystal faces, the lines p- 5 p i -i tvt 

 appeared so fine as to be for the most part indis- 

 tinguishable by the naked eye, but under the microscope showing most 

 beautiful markings, all parallel either to the cube edges or to those of the 

 octahedron. Most of the lines were so fine as to appear like the finest 

 striations, while a few, on the other hand, were coarse enough to be 

 recognized by a pocket lens as consisting of plates with all the char- 

 acters of the finer Widmanstattian figui'es. 



In actual contact with the crystal just described appeared an acute 

 rhombic prism with an angle of about 120°. This prism, shown of 

 twice its size in Fig. 6, could only be separated by the hammer over 

 the area ahcd, and the rest of the face had to be continued by cut- 

 ting through a very compact part of the specimen, ab, be, and cd 

 are the natural crystal edges, and the three faces of the prism not 

 shown in the figure were chiefly characterized by the system of fine 

 lines seen here parallel to cb. The lower of the two drawings was 

 made from the original specimen, without a knowledge of what the 



* Akademie der Wissenschaften Wien, Bd. Ixx. Abth. i. p. 449. 



