280 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII. 



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 a figure. It is a smooth, shining, somewhat undulatory, like a roche 

 moutonnee 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 a figure, 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 slicken- 

 sides. This I have tested by cutting sections at right angles to the surfaces. The outlines of 1 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 con- 

 trary be assigned to the same cause in this meteorite. The conclusion seems fair therefore that these planes and sur- 

 faces 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 

 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 devel- 

 oped in a small body. 



The natural surface of the more conical part (Brustseite) of the meteorite as it is at present joined together, is for 

 the most part deeply pitted with characteristic meteoritic thumb-marks (piezoglypten). These pits vary considerably, 

 as would be expected, in form and size, but still exhibit a certain uniformity. The majority have the form of an elon- 

 gated ellipse whose major axis is about twice the length of its minor. The following dimensions may be considered a& 

 representing a fair average of the size of the pits: Major axis, 3.2 cm. (1.25 in.); minor axis, 1.5 cm. ( in.); depth, 3 

 to 10 mm. (J to f in.). The depression of each pit generally slopes uniformly toward the center of the ellipse, but 

 often there are to be found pits, the deepest point of which is quite eccentrically placed and which have a more or lesa 

 conical shape. Some pits have a nearly circular outline as contrasted with the more common ellipsoidal one. These 

 circular pits are usually of small size, but one of large size and unusual depth is to be found at the point in the 

 meteorite where the two planes A and C cut each other. This pit has for the most part the shape of a deep regular 

 bowl, although the regularity of one portion is broken by two smaller conical pits. The depth of this pit is 3.2 cm. 

 (1.25 in.) and its diameter 6.4 cm. (2.5 in.). The point of junction of the planes is almost exactly at the center of the 

 pit. It is evident that this was a point of weakness in the stone at which the erosive action of heat and friction pro- 

 duced during the passage of the mass through the atmosphere worked more rapidly than on other parts of the surface. 

 Its occurrence at the point of junction of the planes is pretty good evidence that the latter existed in the stone pre- 

 vious to its entry into the atmosphere. This fact has also a bearing on the disputed question as to the origin of the 

 pits in general. It shows that they owe their origin chiefly to an excavation by heat and pressure of the softer or more 

 friable parts of the surface of the mass which is acted upon. Wherever there is a point of weakness there a pit will be 

 formed. Vice versa, where a pit is formed, there was a point of weakness. 



The rear side (Ruckseite) of the stone is not pitted. It has a well-developed crust, but the encrusted surface ex- 

 hibits no marked depressions or elevations. The only portion of the meteorite as now restored which illustrates the 

 Riickseite is that appearing in the upper right-hand part of an accompanying plate. Here the surface is slightly undu- 

 lating, but there are no pits. 



The color of the crust of the meteorite is in general dark brown, but varies from almost black to light brown. At 

 a little distance it appears perfectly smooth and in places shining, but on close examination it is seen to be quite uni- 

 formly and coarsely stippled by the protrusion of the more resistant grains. In many places, especially in the vicinity 

 of the pits, minute threadlike markings appear over the surface, sometimes in parallel and concentric series, but more 

 commonly in arborescent forms which are often quite elaborate. These series or systems of markings do not appear to 

 run in any common direction, but are differently oriented wherever found. I have noted no system more than 1 

 inch (2.5 cm.) in length, but several of about this extent. They resemble closely the lines of flow such as have been 

 noted on the crust of the Stannern and other meteorites, and doubtless are of this nature, being formed by a minute 

 portion of the substance of the meteorite becoming momentarily fused and flowing in a diversified path until cooled. 

 Their course in some cases seems to mark the swirling of the same air currents which formed the pits. More extensive 

 and larger ridges are to be observed over some portions of the crust. Three nearly parallel appear on the portion of 

 the Riickseite just mentioned. Each is continuous for a length of from 3 to 5 inches. These do not appear to be of the 

 nature of the lines of flow above mentioned, but more nearly resemble the veins which stand out on some meteorites 

 and probably mark a line of more highly resistant constituents. Sections cut at right angles to the crust and exam- 

 ined with the microscope exhibit little if any alteration on the crust surface. The mineral outlines seem to be con- 

 tinued sharply up to the edge, and except for a certain smoothness of contour a crust surface could not be distinguished 

 microscopically from the surface of an interior portion. Occasionally a metallic grain protrudes from the general out- 

 line, but so far as the contour as a whole is concerned it appears to be the result of erosion rather than of fusion. 



