56 Professor T. G. Bonney — On Rocks from Ararat. 



the microscope. Its base is a sienna-brown glass, containing 

 numerous felspar microlitbs, witb some grains of hematite, perhaps 

 also of pyi'oxene. In this are plagioclase felspars, much as usual, 

 and some pyroxene crystals, most of which appear to be augite. 



Other Bocks from Little Ararat. 



Three specimens (H). One is a slightly porous, dark rock, with 

 small crystals of lighter-coloured felspar ; another a similar rock, 

 but a little more porous, and the felspar slightly less conspicuous ; 

 both these weather an Indian-red colour, and the latter is slightly 

 streaked with that tint. A third rock is a piece of vesicular scoria 

 of a purplish-bi'own colour, weathering red. The microscope shows 

 the base of the first specimen to be a rather light-brown glass 

 (containing numerous acicular microlitbs and grains of opacite) in 

 which are scattered many felspar crystals of various sizes, up to 

 about 0*11 inch, the larger not unfrequently broken and sometimes 

 full of glass enclosures. There is also some augite, distinct ambly- 

 stegite, and iron-oxide. The larger minerals are pretty clearly of 

 a distinctly earlier date than the final consolidation of the rock. 

 The second specimen shows only varietal differences from the other 

 one ; the glass is rather browner, the felspar crystals do not run 

 quite so large, and augite distinctly predominates over amblystegite. 

 The arrangement of the glass enclosures in some of the felspars 

 suggests that they have been produced by a local melting down 

 rather than by inclusions of magma. The ground of the red streaks 

 under the microscope is a richer red, more like that of G. These 

 two rocks most resemble B, 6, 2. 



General Bemarks. 



So far as we can infer from these specimens, the rocks of Ararat, 

 considering its size, exhibit surprisingly slight differences. They 

 are augite-andesites, varying slightly in the nature of the glassy 

 base, the size of the felspars, the occasional presence of a horn- 

 blende, and the amount of amblystegite, which mineral, however, 

 probably is rarely quite absent. The larger felspars are some- 

 times corroded or broken, and not unfrequently an outer zone may 

 1)6 distinguished, by either containing more enclosures, or being 

 more free from them, or extinguishing at a slightly different 

 angle. The enclosures apparently are of five types — (a) small 

 separate microlitbs or mineral granules, in some cases possibly 

 a pyroxene, (b) very minute belonites, associated in clouds, 

 (c) minute dust, (d) brownish glass, (e) cavities. Where one or 

 more is conspicuous this is noticed above, and I am disposed to 

 regard the glass enclosures as more often results of partial and_ 

 local melting in a crystal owing to in-egularities of chemical com- 

 position than to enclosures of the original magma. 



Aghri Dagh. 



This name is applied to the range of which Ararat forms the 

 eastern bastion, and sometimes even to that mountain. It is nearly 

 100 miles in extent, its peaks rising in one case to more than 



