12 



MEMOIRS NATIONAL ACADEMY OF SCIENCES. 



tVoL.XIV. 



the stage is revolved between crossed nicols. A monoclinic pyroxene is present in minor quan- 

 tity, showing indistinct traces of polysynthetic twinning, and there are frequent interstitial, 

 very irregular areas of calciiun phosphate. It will be noted from Eaktns' analysis that the 

 stone yields 0.41 per cent PjOj, an unusually large amount. I find nothing that I can with 

 safety relegate to a feldspar, even of the maskelynite type. The structure is, however, so 

 obscuie that it will not do to pronounce too definitely on this point. The general resemblance 

 to the McEonney stone is very close, but in composition, as shown by the two analyses below, 

 it differs radically in the proportional amounts of alumina and ferrous iron, a difference which 

 can be explained by the presence of an alimiinous-monoclinic-pyroxene in the stone of McKin- 

 ney, while magnesian forms prevail in that of Travis County. 



Travis 

 County. 



McKin- 

 ney. 



Silica (SiO) 



Alumina (8I3O3) 



Chromic oxide (CrjOj) 



Ferrous oxide (FeO) 



Magnesia (MgO) 



Lime (CaO) 



Manganous oxide (MnO). 



Nickel oxide (NiO) 



Potash (K^O) 



Soda(NajO) 



Iron(Fe) 



Nickel (Ni) 



Cobalt (Co) 



Copper (Cu) 



Sulphur (S) 



Igmtion(HjO) 



Phosphoric acid (PjOi)... 



Total.. 

 Less O for S. 



Percent. 



44.75 



2.72 



.52 



16.04 



27.93 



2.23 



Trace. 



.52 



.13 



1.13 



1.83 



.22 



.01 



Trace. 



1.83 



.84 



.41 



Per cent. 



37.900 



13.290 



1.110 



7.400 



26.690 



1.650 



.210 



.440 



5.070 



.920 



.050 



.004 



'6.260 



.050 



101.11 

 .92 



100.044 



Total. 



' Chromite. 



'FeS. 



It is obvious from the above that the Travis County stone is to be classed — following 

 Brezina — as a black chondrite, rather than a Ckb, as is Bluff. 



It is greatly to be regretted that so little is known regarding the fall or fuxding of either of 

 these interesting stones. 



Waconda, Kdns. — ^This stone has been the subject of several papers and briefer references, 

 of which only those of Shepard, Smith, Wadsworth, and Brezina, are important. Neither 

 Shepard nor Smith made use of thin sections, a method then practically xinknowa, and their 

 determinations of mineral composition were surmises based on chemical analyses. Wadsworth 

 based his brief description evidently on a single section, and there is nothing in Brezina's to 

 indicate that he made use of other means than perhaps a pocket lens. 



As thus far described, the stone is a brecciated crystalline chondrite, or aumaliteof Meunier, 

 consisting of oHvine, enstatite and a monoclinic pyroxene with the usual sprinkling of metallic 

 iron and iron sulphide. Smith's analysis, referred to later, showed it to consist of 3.85 per 

 cent troilite, 5.34 per cent nickel-iron, and 90.81 per cent stony matter. In describing the 

 appearance of the stone he mentioned as occurring "only on one part" of his specimen a mineral 

 ''in the form of a white, crystalline mass, not exceeding in weight 20 milligrams," which was 

 soluble in hydrochloric acid, the solution reacting for magnesia and sihca. This mineral he 

 thought might occupy "the same place among the unisilicates of the meteorites that the ensta- 

 tite does among the bisilicates." 



In looking over a quantity of fragmental material in the Shepard collection my attention 

 was attracted to a small white area, some 2 mm. in diameter, on one of the fragments, and, 

 recalling Smith's work, I undertook its determination. The results are given below, and, as 

 will be apparent, the investigation was much more extended than at first intended. 



In the thin section the stone is at once seen to be composed essentially of ohvine and pyrox- 

 ene with nickel-iron and troilite. The chondritic structure is very evident (Fig. 2, PI. V), the 

 individual chondrules consisting whoUy of pyroxenes or of olivine in the customary forms, 



