172 Field Museum of Natural History — Geology, Vol. III. 



besides circular are oval, semicircular, kidney-shape and pear-shape. 

 The direction of the cavity tends to be at right angles to the surface, 

 but this varies also. Holes similar to these occur in many large iron 

 meteorites, such as Chupaderos and Charcas, and are usually ascribed 

 to a boring action of the air, or to the fusing out of troilite nodules. 

 Their occurrence in the Quinn Canyon meteorite does not seem to 

 throw any additional light on their origin. Their existence must be 

 more or less responsible for the noise which accompanies the fall of 

 a meteorite, for when a current of compressed air is directed against 

 one of them a sharp, ear-piercing sound is produced. What the noise 

 must be from this cause when the whole mass, highly heated, is ad- 

 vancing at an enormous velocity, is almost beyond comprehension. 



Aside from these coarse features of relief of the surface, there are 

 others of a more minute character. These may be designated as struc- 

 ture markings and lines of flow. The structure markings show the inti- 

 mate crystal structure of the iron and are most abundant on the walls 

 and at the bottom of cavities near the apex of the meteorite. They 

 consist of groups of parallel ridges about 1.5 mm. apart, cross-hatched 

 by shorter ridges at right angles. Small square pits about 1 mm. on a 

 side are formed as a result. The long ridges are probably formed by 

 tasnite ribbons. Those at right angles are at irregular intervals, and 

 probably mark the crossing of other bands. As a rule the groups of 

 long ridges run in three directions at angles of 6o° and often intersect 

 to form triangles. The lines of flow as a rule cap the ridges of the 

 meteorite and for the most part follow the crests but also at times 

 cross them in a series of sinuous, more or less parallel lines. The 

 metal is brighter along the lines of flow and in broad patches adjacent 

 to them. They have the appearance therefore of a thin skin of metal 

 which has fused and started to flow at various points. The thickness 

 of this skin can hardly be more than 0.1 mm. The direction of flow 

 is always away from the center of the meteorite, or in other words 

 from the apex toward the base of the meteorite. 



The pittings on the rear side may be divided into two classes as 

 regards size and shape though all are probably similar in origin. The 

 pittings of one class are large and circular or oval in outline. One 

 of the circular pits is 4 inches (10 cm.) in diameter, and the largest 

 oval pit has dimensions of 8 x 8 inches (20 x 13 cm.). Others of the 

 large pittings have less regular shapes but all have sharp edges and 

 do not merge into one another. The pittings of the other class are 

 smaller, dot the surface pretty uniformly and average about one inch 

 (2.5 cm.) in diameter. They show all variations of shape between 



