54 BULLETIN 149, UNITED STATES NATIONAL MUSEUM 



the chondritic character so evident on casual inspection, is not borne 

 out by close study. 



A suggested resemblance to chondritic structure is found in the 

 peculiar drift bowlders found some years ago at Thetford, Vermont. 

 These were described by Dr. E. O. Hovey^^ as resembling conglom- 

 erate the most conspicuous feature of which is the numerous rounded 

 masses of granular olivine scattered through it. In addition are 

 numerous rounded pebble-like grayish green pyroxenes sometmies 

 reaching dimensions of several inches. The pebble form of the last 

 is however wholly assumed, the microscope and thin section showing 

 them to be crystalline secretions partially resorbed. The olivine 

 aggregates are, however, true inclusions in a crystalline ground of 

 augite and feldspars like those in the basalts of the Eifel and Eum- 

 berg, Bohemia; or the meteorite of Parnallee, India. On a gigantic 

 scale the Bohemian examples do bear a resemblance to the chon- 

 droidal forms found in some meteorites as that of Bjurbole. As, 

 however, the groundmass of the basalts is crystalline and glassy 

 there is no real connection. 



Another very suggestive example of an imitative form is shown in 

 Plate 32, Figure 2. The rock is a periodtite from a dike 2 miles east 

 of Raton, N. Mex., collected many years ago by Orestes St. John, 

 and with other collections recently turned over to the National 

 Museum by Dr. Frank Springer. Megascopically the rock shows a 

 dense dark greenish gray, nearly black ground thicldy studded with 

 dark phenocryst and occasional large spherulitic forms and sizes up 

 to a centimeter in diameter. These are of olivine which sometimes 

 break away in form and manner strikingly simulating the meteoric 

 chondrule. 



In thin section the rock is found highly altered but consisting 

 mainly of olivine and a rhombic pyroxene with abundant small 

 octahedra of pleonast and numerous colorless needles with the 

 characteristics of apatite, though their optical properties are wholly 

 obscured by decomposition. An abundant phosphomolybdate reac- 

 tion is produced when a drop of acid ammonium-molybdate is placed 

 upon the slide. The one time presence of a glass base is indicated, 

 but here too decomposition has gone too far for satisfactory deter- 

 mination. It can only be said that numerous interstitial areas are 

 nearly colorless and wholly isotropic. 



The chondritic structure is found to be wholly simulated and is 

 produced by large oval and spherical olivines which have undergone 

 a partial serpentinous and chloritic alteration as shown in the figure. 

 This alteration begins with the formation of a thin coating (border 

 in the section) around the outside and all stages to complete altera- 

 tion of the granule. Such alteration is common, but rarely as in 



18 Trans. New York Acad. Sci., vol. 13, 1893-94, p. IGl. 



