AGENCIES OF METAMORPHISM 413 



and completely enwrapping a chondrule or crystal granule, as the case 

 may be. It is not possible that the temperature during the period of 

 deposition remained sufficiently high to hold the metal in a condition so 

 liquid as to penetrate the stone to this extent. The only alternative is 

 that it was derived from some easily reducible vapor or solution of greater 

 penetrative power and at a probable lower temperature.** It is notice- 

 able, further, that there is in these cases no recognizable corrosion of the 

 silicates, even where the metal occurs in much larger quantity, a matter 

 to which I have elsewhere*^ called attention. It is still further to be 

 noted that in the case of the Cumberland Falls stone the metal occurs 

 also in form of a thin plate lying between the enstatite breccia and the 

 dark chondritic fragment it incloses. In this case at least a portion of 

 the metal was certainly deposited subsequent to the brecciation and com- 

 mingling of the fragments. 



A study of a large number of analyses shows, however, no recognizable 

 relationship in the percentage amount of metal and degree of meta- 

 morphism. 



The tuffaceous meteorites, as previously announced, are considered 

 unquestionably of volcanic origin. That a ferrous chloride is a con- 

 stituent of volcanic emanations is a matter of common knowledge. The 

 products from such emanations from terrestrial volcanoes naturally ap- 

 pear largely in the form of oxides, but in an oxygen-free atmosphere, and 

 particularly one containing free hydrogen, one is justified in assuming 

 ilre reaction FeCl + H = Fe + HCl, Meunier has shown*** that this 

 reaction may take place at a temperature not exceeding 400° centigrade. 

 I can therefore see no reasonable objection to the assumption that such 

 an origin as outlined may be ascribed to the metal in stony meteorites. 

 This idea, I need scarcely state, is not wholly new. 



Summary of Conclusions 



The chondritic meteorites are regarded as of a tuffaceous origin and 

 their crystalline structure, where such exists, as due to metamorphism in 

 which both heat and pressure have taken part. It is pointed out that the 

 most perfect chondroidal forms are found only in those meteorites the 

 fragmental (tuffaceous) nature of which is most prominent, and that 



" Iron melts at about 1500° centigrade, while the figures I have quoted on page — 

 for the fusing points of the silicates range from 1250° centigrade to 1400° centigrade. 

 The conclusion is obvious. 



*■'• On chondrules, etc. Proc. Nat. Acad, of Sciences, vol. 6, no. 8, p. 470. The brec- 

 ciated pallasitic forms, like those of Admire and Eagle Station (Rokiky group), show in 

 an even more marked degree the lack of any corrosive power of the metal. 



^« Meteorites, Paris, 18S4, p. 346. 



