142 THE DESICCATION OF LATER GEOLOGICAL TIMES. 



Russegger, who recognized in the deep gorges of the desert mountains, 

 in the deep Ghors, or torrential stream-beds of tropical Africa, the results 

 of long-continued and heavy rains in former ages. Certainly, at the time 

 when the country was at the height of its prosperity, when it was traversed 

 by numerous canals, when artificial lakes, such especially as Lake Moeris, 

 covered it, when cultivation extended fur beyond the present boundaries 

 of the desert — when all this was the case, certainly the climate must have 

 been very different from Avhat it now is. What mean all those petrified 

 remains of various kinds of trees wliich are so frequently found in Egypt? 

 The tradition that Lower Egypt at least was once an arm of the sea? The 

 once larger area of alluvial plain, and the very much larger water-surfaces 

 exposed to evaporation ? The plants, finally, in regard to which Ave intend 

 to give more details farther on, and of which plants some, like the Nelumbo, 

 require a very moist soil, and which, formerly the pi'incipal article of diet, has 

 now entirely disappeared from Egypt?"* 



Fraas, after a brief discussion of Russegger's ideas in regard to the causes 

 of the desiccation in question, to which we shall have occasion to revert 

 farther on, proceeds to give numerous instances of changes in the distribution 

 of plants, especially of cultivated ones ; which changes have taken place in 

 later geological times, and which seem to him to prove a marked decrease 

 in the amount of moisture. 



Mr. Andrew L. Adams, in his account of an examination of the so-called 

 petrified forest of the Mogattam Hills, writes as follows : " This silicified 

 wood deposit appears to belong to a more recent epoch than the nummulitic 

 rocks, and may be referable to a period immediately preceding the submer- 

 gence of the Sahara and general depression of North Africa just noticed ; or, 

 in other words, contemporaneous with the age when the river flowed over 

 the plateaus of Nubia. No traces of ancient levels or terraces were observed, 

 but about Beni Hassan we could define terraced cliffs on the sides of the 

 long straight glens, also ravines and larger valleys, which may in part have 

 been formed by the denuding influence of the sea, during the oscillations of 

 level, and since farther opened out by atmospheric agencies. No doubt more 

 extended observations would elicit important data in connexion with this 

 interesting subject. Who can tell how far the Egyptian priests erred when 

 they informed Herodotus that at the time when Menes, the first mortal, 

 reigned over EgApt ' all the country except the district of Thebes was a 



* Klinia unci Pflanzenwelt, p. 41. 



