32 SCIENCE PROGRESS 



chondritic stones, all of which approximate to the following 

 type: 



Nickeliferous Iron (Fe/Ni = io/i) 

 Troilite (FeS). 

 Olivine (Mg/Fe =■ 3/1) . 

 Bronzite (Mg/Fe = 4/1) . 

 Oligoclase .... 

 Chromite .... 



• 9 

 . 6 



• 44 



• 3o 

 . 10 



1 



100 



If such a close correspondence were found in a series of 

 terrestrial rocks, they would be said to present a high degree 

 of consanguinity. The evidence points directly to community 

 of origin, both as regards the chemical constitution of the magma 

 from which they crystallised, and the physical conditions which 

 determined their structures. 



It is a noteworthy feature in the fragmental meteorites 

 that no trace of stratification, foliation, or weathering has 

 ever been observed. Moreover, the minerals which require 

 the presence of "mineralising agents" in order to crystallise 

 successfully are one and all absent from meteorites. Olivine is 

 never altered to serpentine, nor felspar to kaolin, or sericite, or 

 epidote. The minerals are throughout fresh and unaltered. 

 These facts may be interpreted as showing that the parent body 

 was lacking in the gases and vapours which would have pro- 

 moted mobility of the magmas and selective differentiation, and 

 that consequently it was devoid of a " crust " such as that of the 

 earth, and was also without an appreciable atmosphere or ocean. 



That the parent body had already cooled well into its interior 

 at the time of disruption is proved in a most striking way by the 

 occurrence of combustible hydrocarbons in certain meteoric 

 stones, and also in a limited but well-defined group of carbon- 

 aceous meteorites. The latter, having a very low density and 

 an unusual composition, may possibly represent whatever 

 " crust " the parent body possessed. The presence of hydro- 

 carbons implies that ever since their formation the meteorites 

 which carry them can never have been subjected to any but low 

 temperatures. During the swift flight through the atmosphere 

 the superficial skin of a meteorite is fused, but its interior, 

 already chilled by its passage through space, remains cold, 

 and so continues to preserve the volatile compounds from 

 destruction. 



