METEORITES OF NORTH AMERICA. 465 



indication of a structure composed of distinct grains. All that is observable is numerous, tiny, closely compacted, 

 brightly glistening points apparently produced by the reflection of light from the walls of inequalities produced by 

 etching. They are in general uniformly distributed; in some of the composing pieces they arrange themselves in such 

 a way as to produce a sort of interlaced striping whose direction varies in each grain. Rhabdite, which according to 

 Brezina is present in oriented form, I did not find, nor troilite nor schreibersite. 



In thin sections the silicate inclusions appear to be chiefly olivine. As also stated by Wadsworth, they are accom- 

 panied by plagioclase, which may be easily distinguished from the olivine by .the double refraction and twinning striae. 

 In one grain the olivine is present only in the central portion and sharply contrasts with a single small bordering zone. 

 Such a zonal formation is seldom observed in the case of meteoric material. According to estimate from five thin 

 sections, plagioclase occurs in such minute quantities that it could not influence the results of analysis in any noticeable 

 degree. Most of the olivine grains consist of a single individual, occasionally spherical in form, in other cases roundish 

 or oval (when as a rule they are twice as long as wide) and measure 0.05 to 0.20 mm. in size. However, they fall some- 

 times as low as 0. 01 mm. and again occur as large as 1 mm. In the case of the larger sizes they are without exception 

 aggregates of several grains, and the resulting form is usually elongated. Isolated grains were observed which consisted 

 of two straight and well-defined individuals, such as to suggest twinning. Moreover, such grains occur very rarely on 

 which are to be seen indications of crystal outlines. The distribution is in general quite uniform and regular; in the 

 case of Carleton, however, the olivines arrange themselves in some portions of the section quite plainly in bent, nearly 

 parallel-line systems, which converge to several centers and are entirely independent of the direction of the boundaries 

 of the nickel-iron grains. Upon the much smaller Ainsa iron specimen this appearance was not observed. In this case 

 also the roundish forms prevail to a greater extent, and the grains are on the average somewhat smaller, although the 

 number is somewhat greater, so that the total amount of olivine in both irons is approximately the same. 



In thin sections the olivine appears quite colorless. Undulatory extinction which is so common in the stone 

 meteorites was not observed . Many grains are free from inclusions, others contain small , spherical to roundish opaque 

 granules (apparently of nickel iron), or colorless inclusions with one or more vesicles apparently of glass. Cracks are 

 noticeably scarce. They are as a rule entirely wanting on the olivines of small to medium dimensions. In the larger 

 grains and aggregations whose number is comparatively small, they are usually quite abundant and run very irregu- 

 larly. A coating of iron hydroxide is quite common; it is due apparently to the thin section, since it was not observed 

 in isolated grains. 



Although in the specimens examined, individual differences between Carleton and Ainsa are observable, it is to 

 be noted that these are very meager, and only to be discovered by very careful comparison, so that they would not 

 serve to distinguish with certainty between specimens from the two localitiea. 



For the purpose qf ascertaining their chemical composition, a larger piece of each iron was treated with cold dilute 

 HC1, in order to separate the olivine from the nickel iron and obtain a sufficient quantity of the former for an analysis. 

 The isolated grains were colorless and sometimes clear as water, sometimes somewhat cloudy, apparently because of 

 the incipient action of the acid. As many grains were grown together with or penetrated by nickel iron, all of this 

 was removed that could be separated by means of a magnetic knife. But not all grains with opaque inclusions could 

 be removed without reducing too much the quantity of material. The heavy portion removed by the magnet or sepa- 

 rated from the olivine by means of methyl iodide, was treated with HC1, and a residuum composed mostly of silicic 

 acid was left; this solution was combined with the principal solution. The proportions were as follows: 



Carleton Ainsa 



Soluble portion 96. 32 96. 61 



Residue (SiO 2 ) 0.82 0.67 



Olivine.. 2.86 2.72 



100.00 100.00 



By J. Fahrenhorst's analysis the following results were obtained (a indicating the totals; 6 the nickel-iron portion). 

 The results obtained for chlorine and carbon in Carleton are inserted in Ainsa. 



Ainsa 



a b 



84. 60 89. 40 

 9. 24 9. 54 



.95 .98 



.02 .02 



.02 .02 



.04 .04 



.01 

 .04 

 .17 

 L76 

 .51 



3.39 



100. 75 100. 00 

 716 15 30 



