STRUCTURE OF METEORITES MERRILL. 183 



may be. The meteorite of Shergotty, India, is a good illustration of 

 this tjrpe (fig. 1, pi. 8). It is, however, not an abundant form. A 

 nearly feldspar-free type closely allied to our terrestrial pyroxenites 

 is shown in figure 2, plate 8, which is from a photomicrograph of a 

 stone which fell at El Nakhla, Egypt, in 1911. 



At least 90 per cent of the stony meteorites belong to the class 

 called by Rose " chondritic," from x°^P ^ a grain, in allusion to 

 the rounded and oval bodies or chondrules which are so eminently 

 characteristic (plates 7 and 8). These chondrules consist at times of 

 minerals of a single species, though sometimes of a number of species, 

 which are embedded in a more or less coherent ground of a clastic or 

 crystalline nature. The chondritic material is usually of olivine or 

 enstatite, more rarely a monoclinic pyroxene, and more rarely yet 

 feldspathic, ferruginous or graphitic. Figure 4, plate 8, is from 

 a photomicrograph of a meteoric stone found near Hendersonville, 

 North Carolina. The single chondrule, as shown, is of olivine with 

 a gratelike or barred structure, some of the bars of which, it will be 

 observed, are curved. It is embedded in a fine, granular ground of 

 olivine, enstatite, and monoclinic pyroxene. 



Other examples of chondritic structure are shown in plate 9. Fig- 

 ure 1 is a not unusual type of chondrule in which the pyroxenes are 

 idiomorphic. These porphyritic forms often present the only ap- 

 preciable amount of pure, glassy base I have thus far observed in 

 meteorites. Often, however, in place of glass, the interstices of the 

 phenocrysts are occupied by a fibrous material evidently of the same 

 mineralogical nature, but not sufficiently individualized to render an 

 optical determination possible. Figure 2 of the same plate shows an 

 enstatite chondrule from the meteorite of Coon Butte, Arizona. This 

 shows a marginal row of independent crystals, but it is to be noted that 

 between crossed nickels the entire chondrule is resolved optically into 

 two portions, the angle of distinction between which is some 30°. 

 Figure 3 from the Elm Creek stone shows a chondrule of enstatite 

 almost perfectly spherical, a not uncommon feature ; others show an 

 indistinctly radiating, featherlike cluster of enstatite which is al- 

 most comparable with the frost crystals formed during cold morn- 

 ings on window panes. In figure 1 from the Parnallee, India, stone, 

 the secondary nature of the metallic iron is shown in the manner in 

 which it encompasses and penetrates the mass of the fragmental 

 chondrule. 



To those at all well informed it must have already been made evi- 

 dent that we have in meteorites some interesting and wide variations 

 in both composition and structure from those found in terrestrial 

 rocks. So far as yet discovered, the meteorites contain no elements 

 unknown to our earth, although the form of combination may 

 be radically different. Schreibersite, lawrencite, oldhamite, daubree- 



