THEORY OF THE EARTH. 135 



four thousand years since they began to be form- 

 ed *. 



The overwhelming of the cultivated lands of 

 Egypt, by the sterile lands of Libya, which are 

 thrown upon them by the west wind, is a pheno- 

 menon of the same nature with the downs. These 

 sands have destroyed a number of cities and vil- 

 lages, whose ruins are still to be seen ; and this 

 has happened since the conquest of the country 

 by the Mahometans, for the summits of the mi- 

 narets of some mosques are seen projecting be- 

 yond the sand f. With a progress so rapid, they 

 would, without doubt, have filled up the narrow 

 parts of the valley, ^if so many ages had elapsed 

 since they began to be thrown into it } ; and there 

 would no longer remain any thing between the 

 Libyan chain and the Nile. Here, then, we have 

 another natural chronometer, of which it would 

 be as easy as interesting to obtain the measure. 



Peat-Mosses and Slips'. 



THE turbaries, or peat-mosses, which have 

 been found so generally in the northern parts of 

 Europe, by the accumulation of the remains of 



* See M. Bremontier's Memoir, 

 f Denon, Voyage en Egypte. 



We might cite in confirmation all the travellers who 

 have visited the western border of Egypt. 



