THE EGYPTIAN PETRIFIED FOEESTS. 321 



But whatever be the chemical forces that have converted the nummulites into 

 flints, these do not remain intact after their transformation. The vicissitudes of the 

 temperature, which beneath these cloudless skies varies so greatly between day and 

 night, cause the stones to chip, strewing vast spaces with their fragments. 

 Occasionally the breakage of these flints is effected in such a way as to give them a 

 perfectly regular form. Thus in a wady of the Arabian range west of Beni-Suef 

 are met, scattered about in considerable quantities, siliceous fragments resembling 

 truncated cones and presenting eight symmetrical facets. 



To the sudden changes of temperature have also been attributed the broken and 

 even-worked flakes that have been found in various prehistoric workshops through- 

 out Egypt. But human labour is so clearly stamped on these specimens that it is 

 quite impossible to confound them with the products of natural causes. In the 

 Libyan desert Zittel sought in vain for any naturally produced siliceous chippings 

 bearing even a remote resemblance to the spear and dart heads worked by the men of 

 the stone age, whether in Egypt, Europe or the New World. Amongst the stones 

 of regular form found in the Egyptian deserts, Cailliaud and Eussegger were the 

 first to call attention to the carnelians, jaspers, agates, and other hard stones pre- 

 senting the form of lentils or discs of various dimensions, encircled by a round ridge 

 somewhat like a ring. The interior of these natural specimens is often disposed in 

 concentric circles, and such concretions are very frequently found associated with 

 fossil wood. 



The Egyptian Petrified Forests. 



By a remarkable contrast, petrified trees are known to occur in many parts of a 

 region where living plants have become so very rare. On the east slope of the 

 Jebel-Mokattara, not far from Cairo, is found, if not a " petrified forest," as it is 

 usually called, or " masts of shipwrecked vessels,'" pierced with holes by phollades, 

 and covered with marine deposits, as the early travellers pretended, at least a number 

 of stems transformed to blocks of flint or chalcedony. But by penetrating farther 

 into the desert we come upon far more extensive petrifications, which might really 

 deserve the name of " forests." In a depression of the Arabian plateau, to the south- 

 east of Cairo, the trunks of trees of all sizes are found in such multitudes that certain 

 tracts are exclusively covered with the siliceous stems or fragments of fossil wood. 



In the Libyan desert, west of the Pyramids, other " petrified forests " contain 

 stems over sixty feet long, with their roots and branches, and even with the bark 

 still perceptible in some places. Travellers have also discovered similar masses of 

 fossil wood in various parts of the Nubian desert, in Senar and Kordofân, and even 

 on the upland plateaux of Abyssinia. In all these regions the vegetable remains 

 so petrified belong to the order of the sterculiacese. In Egypt the prevailing variety 

 is the uichoUa Nihtica, and a species of bamboo obtained horn these forests is also 

 preserved in one of the natural history collections in Cairo. 



Whence come all these stems of petrified trees ? Some geologists have suggested 

 that they may have been washed up by the sea at a time when the Mediterranean 



21— AF. 



