288 Field Columbian Museum — Geology, Vol. I. 



to the edge of that piece. This portion of the plane evidently was 

 not sufficiently developed as a division plane to produce disruption 

 of the piece when the meteorite struck the earth. 



That the three planes described represent a structure which 

 existed in the meteorite before its entry into the earth's atmosphere 

 there can be little doubt. They are too regular to make it possible 

 to consider them planes arising from fracture by shock and there 

 are several other lines of evidence pointing to their preterrestrial 

 existence. The most important of these is that their surfaces are 

 slickensided. The slickensided character of the surface resembles 

 that seen in terrestrial rocks and is illustrated in Fig. 2. It is a 

 smooth, shining, somewhat undulatory, like a roche moutonnte surface, 

 and bears short striae which on the same surface run in one general 

 direction, but take different directions on the three several planes. 

 These several directions are indicated in Plate XLIV, Fig. 2, where 

 one of the fragments is represented as removed. The color of the 

 slickensided surfaces is somewhat darker than that of the crust of the 

 meteorite, but there is no evidence of special heat having been 

 developed by the force which produced the slickensides. This I have 

 tested by cutting sections at right angles to the surfaces. The outlines 

 of the individual grains were found to be sharp and unaltered up to 

 the slickensided edge. 



Since slickensided surfaces on terrestrial rocks are so far as 

 known produced by slow differential movement in the mass under 

 considerable pressure and while in the solid state, they may in the 

 absence of any evidence to the contrary be assigned to the same cause 

 in this meteorite. The conclusion seems fair therefore that these 

 planes and surfaces were formed during the preterrestrial existence of 

 the mass and that the mass must, have been solid in its nature while 

 in space. The three planes which I have described seem to me to 

 resemble the joint planes of terrestrial rocks more than anything else 

 I can think of and give us grounds for asserting the existence of joint 

 structure in the rocks of space. I do not know that well marked joint 

 structure has been observed in any other meteorites except that noted 

 by Meunier in one of the stones of L'Aigle*. This stone he regarded 

 as possessing a joint fissure, but it was not as well developed as the 

 planes of the Long Island stone. 



If the occurrence of joint structure in the Long Island stone is 

 deemed proved, it is significant as pointing to a considerable mass 

 possessed by the body in space. Joint blocks of such size as this 

 would not be likely to be developed in a small body. 



*Fremy's Encyc. Chimique, Tome II., Meteorites, p. 457. 



