METEORITE CRATERS — SPENCER 313 



weight of 440 pounds, excavated in 1932 from a depth of 7 feet inside 

 the smallest crater. They were found in contact and with much flaky 

 rust between and around them, and they are evidently the weathered 

 remnants of a single mass. Immediately around and beneath the 

 iron were broken blocks of rock, while the overlying material was fine 

 grained and free from big stones. This crater (no. 13 on Alderman's 

 map) is only 10 yards in diameter and 3 feet in depth; and in this 

 case the explosion was evidently not sufficient to " backfire " the main 

 mass out of the crater. Around the crater 60 small twisted pieces of 

 iron were found, together with fragments of iron shale, but no silica 

 glass. Excavation of the rather larger 15-yard crater (no, 11) gave 

 a negative result. 



The larger blocks of the Henbury iron when sectioned, polished, 

 and etched show the normal lamellar octahedral structure (Widman- 

 stiitten figures) of a medium octahedrite. In the smaller twisted and 

 curved pieces the lamellae are bent and twisted. Further, the kama- 

 cite is granulated, proving that here the temperature exceeded 

 850° C. Oxidation of the iron has proceeded along the curved 

 cracks, along which the pieces eventually break up. These curiously 

 twisted and curved pieces therefore seem to be weathered remnants 

 of pieces of the iron which were torn, perhaps in a plastic condition, 

 from the main masses by the force of the explosions. The corroded 

 surfaces and the normal internal structure shown by the larger 

 pieces of the iron indicate that these also are only weathered rem- 

 nants of still larger masses, in fact merely the cores to which the 

 intense heat had not time to penetrate by conduction. Pieces of iron 

 shale are also found in abundance around the craters. These, 

 especially when found buried, are sometimes clustered together in 

 the form of " shale balls ", in which occasionally a core of unoxidized 

 iron still remains. 



Silica glass has so far been found only around the largest crater 

 at Henbury, but not in the same perfection and abundance as at 

 Wabar; and, being formed by the fusion of a ferruginous sand- 

 stone, it is less pure. It shows a curious distribution on the ground, 

 for which no explanation can be offered. On the west side of the 

 crater larger cindery and cellular masses and pieces of partly fused 

 sandstone are found close to the rim; while on the east side small 

 tear-shaped drops and threads with a smooth, glossy surface are 

 found along a narrow strip of ground extending eastwards a mile 

 from the crater. 



At Henbury there must have been not a single mass but a shower 

 of large masses of iron that formed the group of craters. The large 

 oval crater, which shows a promontory on its longer side, was 

 doubtless formed by two masses falling close together at the same 

 time. 



