FROM LAGHOUAT TO GHARDAIA. 35 



low and with flat summits, but as the distance from the daya region in- 

 creased, the valleys became deeper, until at Ghardaia the effect was that 

 of low, flat-topped mountains \vith broad valleys between, thus remotely 

 suggesting the topography of southern Arizona. However, in southern 

 Algeria the mountains are not so high nor is the "mesa" (hamada) so 

 extensive as in Arizona. The general level of the daya region is prolonged 

 as the summits of the mountains of this the chebka region, while the valleys 

 are eroded to a new level, that of the plain of the M'Zab. A similar con- 

 dition is seen as one goes from Ghardaia to Ouargla, so that in fact there 

 are several immense terraces, reminders of that remote period when there 

 was more rainfall in this portion of the Sahara than at present. 



Although the drainage to the south of the daya region is well developed, 

 the valleys and mountains run in a rather confused way, so as to give to 

 the fancifully incHned Arab the idea of a net, from which the name "chebka " 

 is said to be derived. 



The country from Tilrempt to Ghardaia is characterized by a continu- 

 ously decreasing amount of vegetation. In place of the country as a whole 

 having a covering, however sparse, as in the daya region, one is apt to con- 

 sider the chebka a barren desert, absolutely devoid of plant Hfe; but closer 

 inspection dispels this illusion and reveals the presence, in the more favor- 

 able situations, of not a little vegetation. 



In the northern portion of the chebka region one sees here and there, 

 on the bottoms, specimens of the jujube and the betoum, as well as Zilla 

 macroptera, Petama spherocarpa, and Coronilla juncea. On the rocks at 

 Settafa, Massart reports finding lichens, the first he had seen after leaving 

 Biskra, However, crustaceous lichens occur on the flat tops of the low 

 mountains by Ghardaia. Massart suggests that the absence of hchens in 

 the Sahara (possibly they are not to be found south of Ghardaia) is because 

 of the intense dryness and the great heat, the temperature of the rocks 

 becoming from 60 to 70° C.* 



At Berriane, one of the M'Zab cities, there are over 30,000 palms of a 

 superior sort, watered from over 400 wells. The surroundings of this oasis 

 are extremely desertic and a casual survey of the route between this place 

 and Ghardaia, 44 kilometers distant, reveals almost no vegetation. Here 

 the calcareous plain of Cretaceous origin, the Chebka, is even more eroded 

 than in the portion farther to the north, and the valleys are \^^der. The 

 soil is a fine clay without an admixture of sand. It is only in the most 

 favorable places, along the washes, that plants are to be found, and here 

 are Deverra chlorantha, Anabasis ariiculata, Gymnocarpon jruticostmi, Arte- 

 misia kerha-alha, Ononis angustissima, Linaria fruticosa, Antirrhinum ranto- 

 sissinia, and Haloxylon articulatum (Massart, loc. cit.). Peganum harmala 



* Dr. Charles Amat, Le M'Zab et les M'Zabites, p. 70, gives a somewhat higher 

 temperature for the rocks of the southern Chebka, placing it at 90° to 100° C, or even 

 higher. 



