I 82 STUDIES FOR STUDENTS 



Slickensides {Harniscli flaclien, Surfaces de frottement. s ) — These 

 may be observed on portions of many meteorites, of which the 

 following may be mentioned among others : Bath, Kesen, 

 Limerick, Lixna, Long Island, Manbhoom, Mocs, Ochansk, Stall- 

 dalen, Tysnes Island, and Zavid. The slickensided surfaces 

 may vary in area from a few square millimeters to those more 

 than a foot square (Long Island). In many cases the surfaces 

 have exactly the appearance of similar ones in terrestrial rocks, 

 being smooth, shining, somewhat uneven, and more or less 

 striated in the direction of movement. In other cases, however, 

 they appear as dark striations on the contact surfaces, or as if 

 the surfaces had been rubbed with a piece of graphite. The 

 slickensided surface may be a broad peneplane with generally 

 parallel striae, or it may be seen penetrating the meteorite in 

 numerous narrow peneplanes following the same general direc- 

 ton at different levels. The surfaces do not always extend in 

 the same direction, however, but in different directions and 

 occasionally nearly at right angles to one another. One surface 

 on the Long Island meteorite has in cross section the shape of 

 a J. The polishing of the surface by the movement which has 

 taken place often brightens the metallic grains so that they 

 shine. Sections cut perpendicular to a slickensided surface 

 show a flattening or elongation of the metallic grains, and even 

 of other minerals along the course of movement, 



Meunier regards the blackening seen on the surfaces as 

 indicating heat developed by the movement, and states that the 

 heat was sufficient to metamorphose a portion of the Mexico 

 meteorite included between two slickensided surfaces, which he 

 examined. The slickensided surfaces examined by the writer, 

 however, give no evidence that the movement has been accom- 

 panied by any high degree of heat, at least enough to produce 

 fusion, for the mineral grains along the surface are simply 

 sharply cut off without alteration. This fact, together with 

 the analogies given by terrestrial slickensides, indicate that the 

 movements which gave rise to the slickensides must have taken 

 place while the constituents of the rock were solid. 



