410 Intelligence and Miscellaneous Articles. 



colour in the upper, and of an olive -green to bluish-grey colour in 

 the lower parts of the excavations. Interspersed in the mass are 

 fragments of more or less altered shale, and a micaceous -looking 

 mineral of the vermiculite group, which sometimes becomes an im- 

 portant constituent of the rock, which also contains bright green 

 crystals of a ferruginous enstatite (bronzite), and sometimes a horn- 

 blendic mineral closely resembling smaragdite. A pale buff bron- 

 zite occurs in larger fragments than the green form of the mineral ; 

 and in the rock of Du Toit's pan an altered diallage is present. 

 Opaline silica, in the form of hyalite or of hornstone, is disseminated 

 through the greater part of the rock-masses ; and they are every- 

 where penetrated by calcite. 



The analyses of the component minerals (given in detail in the 

 paper) show that this once igneous rock is a bronzite rock converted 

 into a hydrated magnesium silicate, having the chemical characters 

 of a hydrated bronzite, except where the remains of crystals have 

 resisted metamorphism. Except in the absence of olivine and the 

 small amount of augitic mineral, it might be compared with the 

 well-known Lherzolite rock. 



The diamonds are said to occur most plentifully, or almost exclu- 

 sively, in the neighbourhood of dykes of diorite which intersect the 

 hydrated rock, or occur between it and the horizontal strata through 

 which the igneous rocks have been projected. The authors compare 

 the characters of the diamonds found in different positions, and 

 come to the conclusion that their source is not very remote from 

 that in which they are now found. 



The mineral above-mentioned as resembling vermiculite is de- 

 scribed by the authors as a new species under the name of Yaalite. 



XL VI I. Intelligence and Miscellaneous Articles. 



ON THE SPECTRUM OF THE AURORA. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 WISH to point out a slight error in a communication from Mr. 



I 



J. R. Capron on the Spectrum of the Aurora, which appears in 

 the last Number of the Philosophical Magazine. Mr. Capron writes 

 as follows : — - 



"From Dr. Watts's 'Index of Spectra' I have extracted the 

 three principal carbon-tube bands or lines ; and they compare with 

 Dr. Yogel's oxygen -tube as under : — 



Yellow. Green. Blue. 



Dr. Yogel's oxygen-lines 5603 5195 4834^ 



Dr. Watts's carbon-tube bands or lines. 5622 5189 4829 



" The 5622 for the yellow line of the tube must be an error. 

 5608 seems to me, from my own observations, nearer its place ; and 

 I calculate 5193 and 4825 for the other lines." 



