254. REPORT— 1875. 



peculiarities are perceived in meteorites which, as strongly as the preva- 

 lence of metallic ingredients, contribute to distinguish them from terres- 

 trial volcanic rocks. The early detection of olivine, and the separation of 

 augitc and (?) labradorite or anorthite (a felspar), in the mcteorito of Juvinas, 

 succeeded more lecently by the distinction of enstatite and olivine aa the 

 major constituents of stony meteorites, and finally (steps which we owe to the 

 chemical separation aiul skilful detection of tliese minerals by Maskclyne 

 with the polarizing microscope) the recognition of enstatite and its ferro- 

 magnesian variety bronzite as the iisual representatives of the " insoluble," 

 combined with the basic mineral olivine as the " soluble " silicate entering into 

 their ordinary composition, forms the substructure upon which the chemical 

 analogy of their composition with terrestrial basalts in the many varieties 

 which are met with among the class of stony meteorites is at present based. 

 A system of structural classification according to the amount and mode of 

 dissemination of the metalhc iron, devised by Daubrc'e for the totality of 

 meteorites, and the distinction of " chondritic '" structure in aerolites or in 

 the stony portions of a great number of meteorites by Reichenbach, forms, on 

 the other hand, a ground-plan upon which their mineralogical description and 

 microscopical examination are conducted, — all aerolites and stony parts of 

 meteorites (with exception, perhaps, more or less, of the carbonaceous 

 aerolites) not of this description consisting in general of finely brecciated, 

 splintered and shapeless, cemented or otherwise consolidated crystalline 

 fragments, those aerolites being termed chondritic which enclose scattered 

 through their mass a number of rounded grains or si^herules. To these 

 ordinary characters of structure and composition many subordinate features 

 are also frequently superadded, as the presence of graphite, troilite, and mag- 

 netic pyrites, magnetite, chromite, schrcibersite, and of some rarer but equally 

 distinct minerals, as azmanitc, oldhamite, &c., and of gases occluded in the 

 metallic portions of the stones ; and, again, the crystalline structure of the 

 latter portions, as exhibited in Widmanstattian figures by etching their cleanly 

 polished surfaces with mercuric chloride or with dilate acids, together with 

 the vitreous or crystalline characters of the spheres or fragments and of the 

 cement composing the non-metallic portions of the meteorite, in the detection 

 of which thin sections of it are employed, and both the microscope and its 

 powerful auxiliary polarized light lend important aid. In all these methods 

 of interrogation and of systematic description great progress has recently been 

 made, to describe at length the various results of which would here occupy 

 too large a space. The sul)jcct has been ably handled by Dr. Flight in a 

 series of articles in the ' Geological Magazine ' of the present year (January- 

 xVugust, 1875), and more than a reference to its copious information in a 

 fifteen years' recapitulation of the united progress of similar investigations 

 need not be offered in this Eepoit as a sufficient recommendation for its perusal. 

 As a separate treatise on the subject to which its further Parts are intended 

 to contribute, it maj^ be indicated as the source in which, since the close in 

 the year 1860 of Dr. Buchner's chronological work on ' Meteorites,' students 

 of this department of science (at least in the English language) will find the 

 readiest assistance for their information and guidance in the recent abundant 

 development of these inquii'ies. 



In the valuable recently commenced Annual llecord of contemporary papers 

 bearing on the progress of Geology, the first volume of which is announced at 

 the present Meeting of the British Association as being nearly completed 

 and ready for immediate publication, the Committee has also the grati- 

 fication to observe, in the Section devoted to Petrology, a copious abstract, 



