340 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
Porphyry is said to occur at Gebel ed Dokhan in the eastern 
desert opposite Memphalit. 
Economical Uses of Porphyry, Trappean and Serpentine Rocks. 
—Many of the vases and sarcophagi of the ancient Egyptians are 
composed of porphyry. Of the serpentine, verde antique and basaltic 
trap, scarabeei and other smaller articles of Egyptian sculpture are 
cut. Large statues of basalt are comparatively rare: a few of the 
largest may be still seen amid the rums of Carnac. A dark-coloured 
granite has been mistaken for basalt. 
Plutonic Rocks.—Granitic rocks occupy but a anil portion of the 
superficies of Egypt, appearing at the cataracts of Syene and in the 
desert, where they constitute the anticlinal axis between the Nile and 
Red Sea, in the latitude of Kossier (about 26° N.). According to 
Mr. Trivin,* granite is seen farther north in the same desert, associated 
with porphyry about the latitude of Benisuef (29° 10' N.), a locality 
which he thinks may have supplied the ancient Egyptians with ma- 
terials for many of the monuments of Lower Egypt. Savary+ men- 
tions quarries of granite and marble between Benisuef and the con- 
vents of St. Antony and Paul, toward the north of the plain of El 
Araba; which probably are identical with the locality noticed by 
Mr. Trivin. Mr. Wilkinson has traced it to lat. 28° 26’ N., where it 
occurs in the peak of Gebel Tenaset, rismg among the limestone rock 
not far west of the range that skirts the Red Sea. He states the 
extreme height attained by the granite in Gebel Gharib, lat. 28° 20! 
N., at 5000 feet above the sea. The islands of Phile and Ele- 
phantine near the first cataracts are almost entirely composed of 
granite, which thence extends into Nubia associated with greenstones, 
porphyries and metamorphic schists. It is penetrated by dykes of por- 
phyry, trap, felspar, and eurite, passmg into a small-gramed granite. 
Relative Age.—With respect to its age, the granite must have - 
been elevated to the surface at a period subsequent to the deposition 
of the inferior sandstone and limestone rocks, which rest on its flanks 
in inclined strata, and prior to that of the superior horizontal sand- 
stone. From the occurrence of breccias along the junction-lme with 
the former rocks, and the entire absence of veims of granite penetra- 
ting them, and of effects of heat, it may be suspected that this plu- 
tonic rock was upheaved in a solid form through once-contmuous 
strata of sandstone and limestone, and subsequently laid bare by de- 
nudation. I carefully examined the latter rocks for imbedded granite 
pebbles, but without success. It penetrates the gneiss in vems. 
Lithological Character.—Lithologically speaking, the granite of 
Egypt passes into pegmatite and all the varieties termed syenitic, 
porphyritic, close-grained, grey and red. That from the cele- 
brated quarries of Syene is usually a large-graimed crystalline variety, 
—composed of crystals of pale red felspar, white transparent quartz 
in grains, dark scales of mica, and a few scattered crystals of horn- 
blende. The granite of Egypt is freer from the decay, the maladie du 
granite, than that of India, arising probably from the peculiarly dry. 
atmosphere of Egypt, which has been mainly instrumental in preser- 
* Travels, vol. ii. p. 41. _-F Egypt, vol. i. pp. 530-1. 
