28 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII. 



meteorite. Approximating to right lines the ridges appear to have been modified in their direction to some extent 

 by the crystalline structure of the meteorite, but even where deviated from their initial direction the tendency to 

 maintain rectilinear directions is apparent. They sometimes cross one another at extremely acute angles. 



While at first sight the ridges would appear to be strictly radial, closer examination, especially when made by 

 stretching a fine thread along them, reveals the fact that they are in reality slightly curved in a common direction, 

 the radius of curvature diminishing as the circumference of the meteorite is approached. They represent, therefore, the 

 arms of an Airy's spiral. This variation from a straight line is approximately 1 in 30 or 1 in 50, and is greatest where 

 the slope from the central boss is the steepest. In only one instance was any variation from the common direction of 

 curvature to the left (Isevo-rotation) observable, and this was in the bottom of the larger of the two marginal pita, where 

 for a short distance the curvature is reversed only to resume its regularity near the edge of the disk. 



Surface markings due to crystalline structure. Beneath the prominent drift scorings the lens seldom fails to reveal 

 the crystalline structure of the metal in regular cross-linings of lesser prominence. These show to the best advantage 

 in the bottom of the deepest marginal pit on the side nearest the center of the mass in the ' ' lee of the wall " of that side. 



Fracture lines. Perhaps in some way connected with the crystalline structure is the series of parallel cracks which 

 course over the front of the meteorite in a direction about parallel to its greatest cross-diameter. These joint-like 

 cracks are observable by the unaided eye * * *. In places they are crowded together, separated by rather uniform 

 space intervals of 1 to 2 mm., and at times they are lined with oxide, especially on the more oxidized side of the front. 



THE CONCAVE SURFACE. 



"Thumb marks." The generally concave surface of the meteorite, as already explained, is in sharp contrast with 

 the convex surface or front. In general aspect it does not differ from the surface of the greater number of meteoric 

 irons, and may be described as undulating, due to the presence of large and very shallow pits ("thumb marks ") which 

 coalesce with one another. 



Oxide scale. Over all this surface of the meteorite is a coating of oxide of iron which varies in thickness from less 

 than 0.5 to about 1 mm. in thickness. Thickest on the side of the most protected hollow of the surface, it hat, scaled 

 off locally and left a series of irregular depressions on the larger pittings of a second order of magnitude. As this edge 

 is the one which corresponds to greater oxidation upon the front, it is probable that some small portion of the oxidation 

 occurred subsequent to the fall, due to the unfavorable conditions for preservation as regards air and moisture. 



On this surface of the meteorite there are no distinct markings observable which can by any probability be ascribed 

 to erosive agencies within the aerosphere. 



Infolding of edges. Of some interest is the apparent folding back of the edges on the concave surface. This infold- 

 ing of the edges appears to have been before observed, and is quite noticeable on the models of the meteorites from 

 Puquios, Chile, and Rancho de la Pila, Mexico. The regular curving of both surfaces of the Algoma meteorite near 

 the edges that are turned back favors the view that this phenomenon is a result of slight bending of the marginal area 

 from the pressure of the compressed air on the front, the greater curvature of the front (over that of the back) being 

 ascribed to the erosive action. 



THE MARGINAL SURFACE. 



The marginal surface of the meteorite in all cases where the front does not meet the back in a sharp line has a 

 very hackly appearance and indicates with little doubt a fracture surface. The more irregular contour of the disk 

 along its margin is for about half its length rounded off by the curved front surface meeting the thumb-marked rear 

 surface. Elsewhere, however, it has just the appearance of the fracture surface of a malleable metal ruptured by 

 tensile stresses, small fibers or horns of metal being still attached to the surface. The small V-shaped notches in the 

 marginal contour are rather striking, and perhaps indicate that there was a shearing component of the stress by 

 which the metal was ruptured. A very thin film of oxide quite unlike the scale upon the back covers the marginal 



area of fracture. 



COMPOSITION AND TEXTURE. 



CHEMICAL COMPOSITION OF METEORITE. 



The chemical analysis of the Algoma iron was kindly undertaken at my request by Mr. Arthur A. Koch, laboratory 

 assistant in quantitative analysis at the University of Wisconsin. Duplicate analyses were made of samples of 5 grams 

 each. The material used for this purpose was in thin plates from the sawed cross section. 



On dissolving in acid, evaporating to dryness, and redissolving, the residue was very slight. After weighing, 

 this residue was treated with hydrofluoric acid, and no gritty substance remained. The analyses yielded results as 

 follows, the iron being in the one case determined by the gravimetric and in the other by the volumetric method: 



1 2 



Iron 88. 60 88. 64 



Nickel 10. 64 10. 62 



Cobalt 77 .91 



Phosphorus .14 .16 



Silica 02 .02 



Sulphur Trace. Trace. 



Copper None. None. 



Carbon None. None. 



100.17 100.35 



