EFFECTS OF MOTION 111 



the surface to the pre-aerospheric and the early aerospheric periods of 

 the meteorite, in which it seems most likely that they were formed." It 

 agrees well also with the theory of meteoritic structure and composition 

 recently stated by Farrington,* a theory which must appeal strongly to 

 all students of petrography as being most in accord with the facts ob- 

 tained from a study of terrestrial rocks. 



In accord with this view is the important observation of Doll,t who, 

 after an examination of a large number of oriented meteorites, of 

 meteorite models, photographs, and published descriptions, lays stress 

 on the fact that depressions are much less common on the front than 

 on the back of meteorites, and that on the back they are broad and 

 shallow conchoidal depressions, either coalescing with one another of 

 separated within the general surface of the back — a structure which 

 Hoernes J has likened to that of the surface of some melting masses of 

 iron, and Nordenskiold § to the cavities in melting icebergs. On the 

 front of meteorites the cavities when present are more irregular and 

 oval in shape, with their longer axes radial, and they have generally steep 

 walls on the side toward the center of the meteorite front. To the 

 writer these observations of Doll are interpreted to indicate that the 

 irregularities on the meteorite back were formed at a higher tempera- 

 ture in a general melting down of the body during its pre-aerospheric 

 period ; the irregularities upon the front, on the other hand, to fusion 

 during its passage through the aerosphere, the steep walls toward the 

 center, as in the case of the Algoma iron, being the contact planes of in- 

 cluded more fusible metals with their host. Furthermore, the reddish 

 brown oxide scale, which so generally covers the back of oriented 

 meteorites and is missing from their front, must be assumed to be 

 formed within the aerospheric period, to which the presumably lower 

 temperature behind the moving body is favorable. 



ACKNOW^LEDGMENTS 



In conclusion, acknowledgment should be made of the able assistance 

 of Professor Charles S. Slichter, who has so well supplemented this paper 

 by his discussion of the problems of flight of the discoid meteorite within 

 the aerosphere, problems which seem to have been overlooked in the 

 study of meteoric bodies. To Mr Arthur A. Koch the writer is indebted 



*The pre-terrestrial history of meteorites. Jour. Gaol., vol. 9 (1901), pp. 623-632. 



fDoll: Zwei neue Kriterien fiir die Orientirung der Meteoriten. Jahrb. d. k. k. geol. Reieh- 

 sanst., vol. 37, 1887, pp. 200-201. 



I Hoernes : Ueber den Meteorsteinfall bei Ohaba, etc. Sitzungsber. Akad. Wissensch., Wien, 

 vol. 31, 1858, pp. 79-84. 



g Nordenskiold : Ueber drei grosse Fenermeteore, Zeitseh. Deutsch Geol. Gesel., 1881, p. 14. 



