1890.] NEW YORK ACADEMY OF SCIENCES. 123 



Silurian or Devonian, the Triassic or chalk periods/' At the 

 base only do these venerable mountains show any trace of altera- 

 tion; thus the Eed Sea has on one side thrown a girdle of coral 

 around Mt. Sinai^ and so in recent times produced a coast 

 district; while towards tlie north the sea during the Cretaceous 

 period has formed the limestone plateau of Et Tih (4,000 feet 

 above sea-level), which stretches across the Peninsula to Mt. 

 Lebanon. 



A very remarkable feature, that does not escape the most 

 careless observer, is the variety and beauty of the colors of the 

 rocks; in the limestone region every imaginable shade of yellow, 

 red, brown, and gray, besides snow-white and quite black, give 

 the barren cliffs a picturesque appearance which photography 

 unfortunately fails to reproduce; in the granite region this gray 

 crystalline rock is traversed in all directions by dikes of eruptive 

 diorite, varying in color from black to green and brick-red. In 

 Wadi Tarfa I counted nine narrow red and green dikes in a space 

 of twelve feet. Elsewhere the dikes varied in width from two 

 inches to thirty feet and more; sometimes the red porphyry tra- 

 versed the green, and sometimes both lined the same fissure in the 

 granite. The colors are as well-defined as those on a geological 

 map, and combining with the strong atmospheric coloring of 

 an almost cloudless sky, that produces bright lights and deep 

 shadows in the foreground and an indefinable haze on the distant 

 mountains, together with the deep blue of the mis-named Eed 

 Sea, produce an incomparably artistic effect. (Specimens of red 

 and green diorite.) 



Sand. — The main object of my journey being a search for 

 sonorous sand, my attention was naturally directed to the occur- 

 rence of sand in general. Large banks of blown sand are char- 

 acteristic features in the Nile valley, in the Libyan desert, and 

 in the Peninsula. On the railroad from Ismailiya to Cairo, the 

 authorities have found it necessary to construct long barricades, 

 like our snow-fences, to prevent the drifting sand from burying 

 the track out of sight. In the Nile valley, the fine and dry sand 

 has kindly done great service to archaeologists; blown into un- 

 derground galleries used for sepulture, it has preserved intact 

 the artistically decorated walls. Opposite Assouan, Sir Francis 

 Grenfell has recently opened a score of tombs in which the 

 paintings are as brilliant in color and polish as when completed 

 by the Egyptian workmen centuries before. 



As already intimated, loose sand into which the feet sink is 

 confined to the bottom of deep wadis (Tarfa, Es-Sleh, etc.) 

 inaccessible to high winds, and to banks resting on compara- 

 tively level expanses (Gizeh, Ismailiya, etc.) or on the flanks of 

 hills (Jebel Nagous, etc.). In Wadi Feiran, near its entrance 



