62 Prof. G. H. F. Ulrich. On a Meteoric Stone 



Fig. 3. 



sr 



grain cracked in the manner shown. The oblong grain near the lower 

 margin indicated by a dotted line and the letter e is enstatite. It 

 shows strongly marked cleavage-cracks obliqne to its ontiines, polar- 

 ises in low colours, ranging between light brown and grey, and 

 extinguishes parallel to the cleavage- cracks. The remainder of the 

 section is constituted of finely and coarsely granulated olivine, polar- 

 ising aggregately, and enclosing a number of particles of nickel-iron 

 and dark grains, the largest one of which, near the centre of the sec- 

 tion, is probably oxidised nickel-iron, as it shows minute metallic spots 

 in reflected light. A porphyritic structure, similar to that noticed in 

 the previous section, is seen in the finely granulated olivine portion 

 along the left-hand margin, the larger olivine grains, each of indepen- 

 dent optical orientation, shining out brilliantly in polarised light from 

 the duller fine-granular part. In a grain, indicated by (oa), near the 

 upper margin, a fine optic axis is disclosed in convergent polarised 

 light. 



Fig. 4. — This shows a large chondrule, mainly composed of olivine, 

 rather rudely defined by a border of particles of nickel-iron and dark 

 grains, most of the former occurring around the left-hand margin. 

 The portions of this chondrule left clear, i.e., unshaded, consist of the 

 water-clear, doubly refracting substance, resembling glass. A large 

 amount of this occurs along the right-hand margin, smaller portions 

 around the left-hand margin, and within the mass of the olivine, and 

 it also fills the large rudely-parallel longitudinal fissures, and some 

 large irregular transverse cracks by which the latter is divided. 

 Whilst portions of it are perfectly clear between crossed nicols, others 

 are dark; but on rotation of the stage the extinction travels in an 

 undulating or cloudy manner over the light portions, and those dark 

 before become light. The contrast between it and the olivine is 

 especially well marked during the rotation, as the latter mineral, 

 though much stained with hydrous ferric oxide, polarises in splendid 



