COMPOSITION AND. STRUCTUKE OF METEORITES 27 



6. Kugelchen cJiondrites . This large group consists of very numer- 

 ous well-developed chondrules embedded in (1) a tuffaceous ground 

 which is almost wholly of chondrules and (2) one in which the ground 

 is so loose and friable that the chondrules are readily broken away. 

 There are transitional forms into the next. 



7. Crystalline chondrites, consisting of a crystalline ground in which 

 the hard chondrules are firmly embedded. 



8. Carbonaceous cJiondrites, consisting of black ground due to car- 

 bonaceous matter, and carrying but little metal; hence noted for lack 

 of density. The Orvinites differ in showing a fluidal structure, the 

 crystal Tadjerites are part glassy ground and the Ureilite crystals are 

 black, sometimes chondritic, sometimes granular masses consisting 

 mainly of olivine and showing transitional forms into the group 

 classed under nickel-iron with silicates. 



Obviously such a system of classification permits of no sharp dis- 

 criminations. That of Prior, given below, has much to recommend 

 it in this regard. In this the chondrites are separated according to 

 the true character of their prevailing pyroxenic constituent as follows : 



(a) Enstatite-chondrites. 



(&) Bronzite-chondrites. 



(c) Hypersthene-chondrites. 



To the members of each of these groups are applied the qualifica- 

 tions according to color (white, intermediate, gray, black); structure 

 (crystalline, spherical, brecciated, veined); and composition (car- 

 bonaceous, etc.), used in the Tschermak-Brezina classification. 



As illustrative of a pronounced type of a spherulitic or kugelchen 

 chondrite reference may be made to the stones of Allegan, Michigan; 

 Selma, Alabama; and Bjurbole, Finland, Figures 1 and 2, Plate 18, 

 also Plate 25. These stones are very friable, so friable indeed that 

 thin sections can be prepared only with difficulty. Under the 

 microscope they show in a marked degree the tuffaceous structure 

 characteristic of their class. Tlii'ee or more types of chondrules are 

 not infrequently present in the same stone, (1) the ordinary enstatite 

 chondrule showing in a section a fan-shaped radiating structure; (2) 

 others composed of olivines, sometimes quite idiomorphic developed 

 in a black glass; and (3) dense structureless forms consisting evidently 

 of enstatite. These are all sharply differentiated from the ground and 

 break away from it readily. The groundmass is itself a confused 

 admixture of olivine and enstatite particles with interspersed metal, 

 metallic sulphide and chromic iron, the silicates being almost univer- 

 sally of a fragmental nature. Much of the interstitial material is so 

 fine and dustlike that it is practically impossible to determine its 

 nature in the section, but when isolated it is found to consist of 

 fresh and sharply angular splinters of olivine and other silicates. 

 59587—30 3 



