1905.] NATURAL SCIENCES OF PHILADELPHIA. 881 



the front of the meteor above referred to, from almost the instant the 

 meteor became visible.^ These fragments would naturally soon fall 

 behind the meteor, and in the case which is the subject of this paper 

 probably reached the earth after the collision had taken place and all 

 of the material had been thrown out from the crater produced by the 

 impact. The same would be true of the first "shale balls" to be 

 detached, the origin of which, it seems to me, can be explained as 

 follows. As the front surface became more heated it is possible that 

 fewer of these irons would be thrown off, and almost certain that some 

 of the iron would be melted and would naturally run back to the sides 

 or to the rear surface of the meteor, from which from time to time it 

 would be detached. This burning iron would then drop behind, as in 

 the case of the meteor observed by Mr. Holsinger and myself, and form 

 the shale balls above referred to. On this theory the laminated struc- 

 ture which I have spoken of is possibly due to the fact that the melted 

 iron ran back over the meteor to its rear surface, or at least to its sides, 

 and was detached therefrom in a pasty condition. This would seem to 

 offer an explanation of the five flaming drops which I saw falling be- 

 hind the meteor in April, 1904, and why they were not seen until the 

 meteor had been visible for an appreciable length of time. 



These shale balls probably contimied to drop off from the great 

 Canon Diablo meteor, referred to in this paper, until the very moment 



' Since writing the above it has occurred to the author that the pieces of metaUic 

 iron, and the pittings known as "thumb marks" which they show, are due to the 

 very high temperature developed by friction against compressed air in passing 

 through the earth's atmosphere. Dr. Mallet has confirmed this, and points out 

 that in the case of iron meteorites this temperature would of course be still fur- 

 ther raised by burning. He has also told me that this is a commonly accepted 

 theory of the cause of these characteristic pittings. The effect of this furious 

 burning, produced by the friction against the compressed air ahead of the flying 

 iron meteor, would probably be to make great irregular cavities or furrows on its 

 surface, as in the case of the 14-ton Willamette meteorite described by Mr. Henry 

 A. Ward in the Proceedings of the Rochester Academy of Science, Vol. 4, pp. 137-149, 

 plates 13-18. Whether the spaces represented by such cavities or furrows were 

 once partly filled with nodules of troilite is not of importance in this connection. 

 Having this action in mind it can readily be seen how these furrows or cavities in 

 meeting might cause unconsumecl pieces of metallic iron to be liberated, which 

 would then fall behind the main body of the meteor and still burning reach the 

 earth after the collision. Not only "thumb marks" but so-called "ring" me- 

 teorites are perfectly explainable on this theory. It receives very strong support 

 from certain iron specimens which have recently been found by us (and since this 

 paper was written) in the trench for the pipe line between Cafion Diablo gorge 

 and the crater. To these specimens when fovmd a large amount of magnetic oxide 

 of iron or iron shale was still firmly attached, and occupied the "thumb mark" 

 pittings on the specimens as well as being adherent to the more or less flat sur- 

 faces. When it is found in the pittings, generally referred to by the term of 

 "thumb marks," it is distinctly shaly in character and is seen to curve upward 

 from the bottom of the cavity. There is much to recommend this theory, but 

 may there not be truth in both this theory and in the one just mentioned? 



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