286 
PROFESSOR T. G. BONNET ON A COLLECTION OF 
specks of a hornblendic or chloritic mineral, with grains of quartz and felspar, some of 
which show the twinning of plagioclase. 
Pdiyolites of a purplish colour, exhibiting fluidal structure, and of the former type, 
occur among the boulders on the plain between Girgha and Omhari, and pinkish 
quartz-felsites come from the extreme north-west of the Girgha range, where, in the 
ascent of a valley from the Hadibu plain, “ red granite, white granite, reddish 
felstone, and intrusive dark rock, alternate one with another with marvellous rapidity, 
and disappear under the limestone on the northern side.” One of the quartz-felsites 
[4285] under the microscope exhibits a rather irregular cryptocrystalline structure, 
approaching corailoid or aborescent, here and there spherulitie; the splierulites having 
an irregular outline. The slide is stained with ferrite, contains a few scattered grains 
and imperfect crystals of quartz, decomposed felspar, with microliths of iron-peroxide, 
and hornblende or tourmaline. From the group of compact felsites or rhyolites, 
which are members of a very variable series of rocks near Gedidery, one of the most 
compact, of a purplish colour [4364], exhibits under the microscope a clear base, inter¬ 
spersed with minute aggregated granules of ferrite, varying from a sienna-brown 
colour to almost black, which gives a mottled aspect to the slide. Scattered in this 
are crystals of sanidine and plagioclase (? albite), and other crystals, now occupied by 
yellowish-brown secondary minerals and clotted ferrite, but which, judging from their 
outlines, have in some cases almost certainly been augite, others, however, may have 
been biotite. The felspar crystals have a curiously rounded outline, and contain 
numerous enclosures of brown glass. No free quartz is visible, so that the rock must 
be classed with the sanidine trachytes. The compact red felsites intrusive in granites 
“from the side of Khor, near the village of Gharrieh,” are very much of the normal type, 
compact reddish or pinkish felsites, containing minute specks of quartz and of a 
greenish mineral, with small felspar crystals. [4359], examined microscopically, 
exhibits one of the slightly “ arborescent ” cryptocrystalline structures already noticed, 
and is clearly related to types described above. [4350], from the same region, is very 
closely related to the vein-granites in structure. The ground mass is microcrystalline; 
the quartz, which occurs in irregular grains of variable size, has many microlithic 
enclosures; there are one or two distinguishable crystals of orthoclase, and clusters of 
small crystals of biotite. 
Several specimens of compact felsites or rhyolites have been brought from the dis¬ 
trict to the west of Kittim and then north-north-west as far as Azorah, •where these, 
together with a conglomerate or agglomerate containing a similar rock, form a large 
part of the hills of this district. Ten slides have been examined microscopically, but 
after what has been already said it will be needless to do more than indicate their 
distinctive features. [4443] and [4482] are microcrystalline and exhibit an imperfect 
micrographic structure, the former having a more porphyritic structure. It contains a 
good quantity of plagioclase (? albite) among its felspars and a few specks of decomposed 
grown mica. [4458], [4472], and [4473] are reddish rhyolites with a cryptocrystaliine 
