MERRILL AND TASSIN] THE CANYON DIABLO METEORITES 21 5 



EXPLANATION OF PLATES 



Plate XVIII 



Fig. i. A typical "shale ball," consisting of a residual nucleus of metallic iron 

 surrounded by a crust of iron oxide, to which are adhering frag- 

 ments of sandstone and limestone. The crust has been broken 

 away at the right just above the center, exposing a portion of the 

 nucleus. (Cat. No. 76,843, U. S. N. M.) 



Fig. 2. A shale ball similar to that shown in Fig. 1 cut in halves, showing the 

 metallic nucleus with its crust of "iron shale." The dark marginal 

 areas are due to the exudation and oxidation of iron chloride after 

 cutting. (Cat. No. 76,842, U. S. N. M.) 



Plaice XIX 



Shale ball cut in halves to show structure of the metallic nucleus and to illus- 

 trate the rapid oxidation which takes place along the outer margin. 

 In the plate the two halves are oriented as laid open by the saw, the 

 oxidation products and adhering rock fragments having broken 

 away somewhat unequally. The outline between the metallic and 

 oxidized products is very conspicuous. Fig. 1 shows a freshly 

 polished surface, while Fig. 2 shows the second half after being for 

 some days exposed to the air. The illustration shows the rapidly 

 oxidizing ferrous chloride as it exudes around the outer margin. 

 (Cat. No. 76,946, U. S. N. M.) Dimensions of metallic nucleus, 88 

 millimeters by 187 millimeters. 



Plate XX 



Etched slice of the common type of Canyon Diablo iron, showing the thick 

 plates of kamacite and nodules of troilite. At upper right a small 

 area of transition toward the structure of the shale ball iron. 

 (Cat. No. 85,833, U. S. N. M.) 



Plate XXI 



Six characteristic pieces of the smaller Canyon Diablo irons of the common 

 type, selected to show forms and lack of fusion effects on sharp 

 angles. All reproduced on same scale. Actual length of central 

 specimen, 170 millimeters. (Cat. No. 76,841, U. S. N. M.) 



