138 Prof. Maskelyne and Dr. Lang's Miner alogical Notes. 



line system, would seem to confirm the view of its being olivine, 

 and help to show that Manegaum, like the other Howardite aero- 

 lites, is mainly composed of that mineral. Like these other stones, 

 it contains this olivine ingredient in grains of some considerable 

 size, larger grains, indeed, than are usually met with among the 

 constituent minerals of aerolites. They, however, are seen to be 

 present in every gradation of minuteness, and the whole are 

 cemented together, or rather are loosely entangled in a sort of 

 network of another remarkable mineral, the same probably which 

 Rose has hypothetically described as anorthite. 



It is, however, very unlike the anorthite as seen in the micro- 

 scope in Juvenas, Stannern, or Jonsac, and seems by no means 

 a characteristic feature of aerolites which the calculations of the 

 chemist would proclaim to be rich in that felspar. It presents, on 

 the other hand, a remarkable resemblance to the opake parts of 

 trachytic and porphyritic rocks, such as those of the Drachenfels 

 and the Perlenhardt, or of the bluish Andesitic porphyry of the 

 Esterels. Probably the opake portions of the felspathic ingre- 

 dients of granites, in exhibiting much similarity with these, give 

 a further ground for the attribution of a felspathic nature to this 

 substance. 



It is a remarkably opake, white or yellowish-white mineral, 

 and occurs as an ingredient in a considerable number of aero- 

 lites. Sometimes as a flocculent or curdy network, sometimes 

 in opake round spherules, and often, too, in irregular pieces that 

 look like fragments of these last, or, again, deposited along 

 laminae in crystals of other minerals, it appears to be a very com- 

 mon though a sparsely distributed ingredient of every different 

 variety of aerolite. In Manegaum (and even to a greater degree 

 in Massing) it rises into a somewhat important constituent of 

 the aerolite — which indeed consists almost exclusively of the 

 olivine-like substance I have described, with some of this floccu- 

 lent mineral. There is present also meteoric pyrites (or, as we 

 must now call it since Hofrath Haidinger's recent interesting 

 notice, Tro'ilite*) in a small amount ; and a mineral which 

 seems certainly to be chromite forms veins or reticulations and 

 little dark bands here and there, in which its opake and crystal- 

 line particles are sprinkled, as it were, through the other ingre- 

 dients, and which imparts to these portions of the stone the bluish 

 cast to which allusion has been already made. The crust is 

 of a very rich brownish black, and is tolerably thick, but devoid 

 of the lustre peculiar to what may be called the " enamel" on the 

 Eukrite aerolites. No iron is perceptible in the small pieces I 

 have had the opportunity of examining ; but a negative argument 

 of this kind would be a very fallacious one, as I have found 

 * Sitzungsber. der Akad. der Wissensch. Wien, March 1863. 



