4 PROCEEDINGS OF TEE NATIONAL MUSEUM vol.73 



silicates Mg2Si0.t and FenSiO^ which under the reducing action of 

 hydrogen, carbon'^ monoxide, or hydrocarbons have been reduced 

 and differentiated with the separation of the metal and silicate min- 

 erals, however applicable in cases of direct crystallization from a 

 molten magma, are scarcely so in the cases of the clastic rocks here 

 under discussion and may be passed over. Moreover the suggestion 

 of Fletcher already quoted, still holds good. 



Ideas expressed by Dr. W. Walil with reference to brecciated struc- 

 tures such as are shown by the Deesa and some other irons are of 

 interest. He says : 



Wie aus der vorhergebeucieu Besclireibung ersicbtlicb ist, bat der Silikatan- 

 teil unbebindert von dem Metallteile des Gesteins krystallisiert ; er bat sich 

 wie innerhalb der Hoblriiume eines Scbwammes, dessen Geriist der metalliscbe 

 Aiiteil war, verfestigt. Aber zur Z;'it der Verfestigung der zwiscber.liegenden 

 Silikatmasse muss das Metallgeriist nocb selbst fliissig gewesen sein, deim die 

 Silikate siud dem Metall gegeiiiiber scbarf idiomorph ausgebildet und hier- 

 durcb erhielten die Bisenteile ibre zackige Begrenzung. Es bat folglicb das 

 Magma, aus dem der Siderolitb bervorging, vor dem Erstarren aus einem iuho- 

 mogenen Gemiscbe zweir Fliissigkeiten bestanden, die sicb nocb nicbt eii<mischt 

 batten und von denen die eine aus den Plagioklas- und Pyroxensilikaten, die 

 andere aus fliissigem Metall und Metallverbinduugen (gediegen Eisen mit 

 Cobenit und etwas Scbreibersit? Magnetkies und etwas Magnetit?) zusam- 

 mengesetzt wareu. Die versobiedenen Proportionen zwiscben dem metalliscbeu 

 Anteil und silikatanteii erkUiren sicb dann durcb eine teilweise Entmiscbung 

 und durcb ein Zerbrecben von scbon auskrystallisierten Silikat-partien sowie 

 Hineingeraten derselben in den nocb fliissigen metalliscben Anteil. In dieser 

 Weise eutstand moglicberweise das von Daubree bescbriebene Stiick. [1. e., tbe 

 Deesa Iron.] 



The inference here is that the metal is in a condition of fluidity 

 such as could be imparted only by heat. If so the matter is cer- 

 tainly open for further discussion. That it is possible the meteorites 

 of the pallasite group may result from the direct cooling of two 

 immiscible liquids, the metal, owing to its higher fusibility, cooling 

 first and inclosing the gradually solidifying silicate drops, need not 

 here be argued. That, however, the brecciated structure shown in 

 Figures 3 and 4, or the deposits of metal in the interstices of the 

 silicates as in 1 and 2 could thus originate is doubtful. 



There is in this connection a view relative to these metal-silicate 

 breccias, belonging to the Rokicky group, that ma}^ be worthy of con- 

 sideration, and in which the question of the origin of the metal 

 itself is not necessarily involved. Is it not possible that this breccia- 

 tion may be due to pressure acting upon the mass of a normal palla- 

 site after solidification rather than when the metal is in a fluid con- 

 dition, as Doctor Wahl's paper implies? The metal, being the more 

 plastic, would flow, while the silicates would be crushed. In this 



*^ The possible instrumentality of carbon as a reducing aeent wa.? also considered by 

 Nordeuskiold in the paper already noted and the idea dismissed as improbable. 



