404 G. p. MERRILL ON METAMORPHISM IN METEORITES 



Liiiek,-- ill his discussion of the mineral in the Meuselbaeh stone, says: 



"Icli wiederliole imr vmd betone es, dass die Structur dieses Gesteiiies mit 

 Tuffbildungen wenig oder nichts gemein hat, dass sie vielmehr auf Erstarrung 

 aus dem Schmelzfluss hiuweist, deren letzter Act sich selir rasch A'ollzog, so 

 dass ien verhaltiiissmassig leicht sclimelzbares, den Krystallisationsruckstand 

 bildendes Natronltalsilicat nicht mehr zur Krystallisatioii gelangen koniite."' 



Borgstrom,-^ as late as 1904, wrote : 



"The occurrence of tlie maslielynite between the cliondrules and crystals of 

 olivine and eustatite and close to troilite and nickel-iron forbids an interpre- 

 tation of it as a refused feldspar. The maskelynite in the meteorite from 

 Shelburne is a true mineral species and no alteration product." 



With these opinions the present Avriter can by no means agree. In my 

 own mind there are but two possible alternatives regarding the substance : 

 Either (1) the stones in which it occurs are direct products of the cooling 

 and crystallization of a molten magma, in which case the maskelynite 

 may, perhaps, be a residual feldspathic glass or an altered feldspar, or 

 (2) they result from the accumulation and compacting of already solidi- 

 fied particles — that is, are clastic or tuffaceous — in which case the mas- 

 kelynite must be secondary and due to metamorphism. Its form and 

 mode of occurrence admit of no other conclusion,-* as noted by 

 Tschermak. Indeed, the habit of this substance in occupying the irreg- 

 ular interstices of the magnesia-iron constituents and its common occur- 

 rence in the white, gray, and intermediate chondrites, together with its 

 almost entire absence in the unaltered "kugelchen" forms, is one of the 

 strongest arguments in favor of its secondary origin, through the meta- 

 morphism of a tuffaceous stone of the type of Allegan or Bjiirbole. 

 Borgstrom's objection to this, based on its occurrence in close juxtaposi- 

 tion to troilite and nickel-iron, I can not regard as well founded, since 

 both of these substances are themselves secondary (see page 412) and may 

 have been formed at an entirely different period and under different con- 

 ditions. The fact that either substance occurs not infrequently enwrap- 

 ping a chondrule, would suggest at least that they were the very latest of 

 the products of solidification. 



It is to be noted further that this "glass" never shows the slightest 

 traces of the shattering which is so characteristic a feature of the other 

 minerals and which is variously ascribed to pressure or abrupt. changes 



2^' Ann. k. k. Natui-hist. Hofmnseums, Band 13, 1898, s. 113. 



23 Trans. Royal Soc. of Canada, 1904, pp. 91-92. 



2^ It Is a trifle singular that Borgstrom, after having made the statement quoted above, 

 should describe the Shelburne stone as a veined gray chondrite — that is. as composed of 

 compacted, already solidified particles. The two statements, as I view this matter, are 

 contradictory and irreconcilable. 



