METEORITES OF NORTH AMERICA. 71 



Oxygen ratios are as follows: 



Rammelsberg. Smith., 



b b 



SiO a 31.38 32.11 



A10 a 1.30 



MgO 14.241 15.7 



S&:::::::::::::: S 



K 3 0.12J 



My investigations and those of Smith show, accordingly, that the mass as a whole is a bisilicate, and the former 

 had much purer crystal masses at his disposal. 



It may accordingly be concluded with certainty that the principal part of the stone from Bishopville is enstatite= 

 MgSi0 3 (Si0 2 ,60# ; MgO, 40%). 



Besides this, by far the most prominent constituent, there appears to be present something of an aluminous silicate, 

 which probably proceeds from lime and alkali. But this, as already remarked, is not feldspar, not anorthite, nor 

 are the white grains which Shepard took for anorthite to be so considered. Washing the finely pulverized stone indi- 

 cates that more aluminum and lime and less magnesia are contained in the lighter portions than in the heavier. But 

 concerning the nature of the silicate further investigations must decide. 



The stone from Bishopville contains very little meteoric iron indeed, which, moreover, is mostly oxidized and has 

 produced specks of rust in the mass. Magnetic pyrites and chrome iron are also present, as well as calcium sulphide 

 (oldhamite) (noted by Maskelyne in the stone from Busti). 



Maskelyne I0 suggested that the yellow grains in Bishopville were oldhamite. 

 Wadsworth u gave the following optical study of the meteorite: 



Through the courtesy of Mr. John Cummings and the curator of the Boston Society of Natural History I have 

 been permitted to make a microscopic examination of a small portion of this meteorite, now deposited in the collection 

 of that society. The portion examined is a grayish-white mass resembling, as Shepard remarked, a grayish-white 

 granite (albitic), with brown and black spots. Under the microscope it is seen to be composed of an entirely crystalline 

 mass of enstatite, augite, feldspar, olivine, pyrrhotite, and iron. The structure is essentially granitic, and it appears 

 to belong to the gabbro (norite) variety of the basalts as defined by myself in "Science " for March 9, 1883. 



The enstatite is clear and transparent. It shows a longitudinal cleavage parallel to the line of extinction, and in 

 some specimens this is crossed by a cleavage at right angles. It also has a cleavage which is often well marked and 

 breaks the mineral into rhombic forms with angles, as approximately determined by several measurements, of 73 

 and 107. The principal cleavage is parallel to the longer diagonal of these rhombs. It is this rhombic cleavage, 

 probably, which has led observers to believe that chladnite crystallized in the monoclinic or triclinic systems. 



The enstatite is found to contain many glass inclusions with polyhedral outlines, the planes being presumably, 

 as is usual in such cases, the planes of the inclosing mineral. While many are arranged in the enstatite parallel to the 

 cleavage planes, others are placed at every angle with those planes. The glass inclusions carry bubbles, microlites, 

 and rounded lenticular forms. The last are frequently at the end of the inclusion, and in some cases show the cherry- 

 brown color of some chromite. This material, besides forming inclusions in the glass, is in lenticular and irregular 

 rounded grains in the enstatite itself. It sometimes extends in a series of grains across the entire enstatite mass and 

 at others is in isolated forms. These inclusions microscopically are seen to be composed of a center of nickeliferous 

 iron or pyrrhotite, surrounded by a band of dark material, chromite or magnetite possibly. These ferruginous materials 

 are in many cases surrounded by a yellowish-brown staining of iron which sometimes extends over a considerable 

 portion of the mass and along the fissures. Along one plane in the enstatite numerous vacuum or vapor cavities were 

 observed. The inclusions are seen to be crossed and cut by the cleavage and fissure planes of the enstatite, showing 

 that they were of prior origin to the fissures. 



The feldspar stands next in abundance to the enstatite and is in irregular masses held in its interspaces. It is 

 water clear and almost invisible by common transmitted light. Much of it is seen to be plagioclastic ; but the twinning 

 bands are so exceedingly fine and the polarization of colors so bright it does not as a rule show well this character, 

 except with high powers and when the mineral is near the point of extinction. The feldspar contains numerous 

 yellowish-brown, dark, and almost colorless inclusions, sometimes irregularly scattered but more commonly arranged 

 along planes like the fluid inclusions in quartz. These glass inclusions are of various dimensions and many contain a 

 small bubble. Some microlites were also seen. 



In the feldspar at one end of a section the enstatite was found in minute crystals extending outward from a center 

 forming stellate or rosettelike forms. The structure is like that observed in terrestrial rocks in minerals formed from 

 alteration or solution. This apparently might have been produced in this case, either by the rapid crystallization of 

 enstatite material of a liquid feldspathic mass or by secondary alteration through water action on the rock itself. The 

 absence of any other signs of alteration, except in the ferruginous materials, seems to negative the latter supposition. 

 The ferruginous alteration can probably be accounted for by the absorption of moisture by this friable fissured stone since 

 it reached the earth. The bands of inclusions were seen in several instances to extend from the feldspar through the 

 enatatite, and in one case pass into another feldspar on the opposite side. This indicates that the cause of these inclu- 



