46 NOTES OF A NATURALIST. 



square yards absolutely without a sint^le plant. About 

 Suez, and on parts of the isthmus where a slight 

 infiltration from the sweet water canal has not 

 developed a more varied vegetation, the number of 

 species in a given tract is often very limited ; but 

 tufts of vigorous growth, especially of the salt-loving 

 species, are seen at frequent intervals. On the plateau 

 of Payta, where, as we rambled about, several pairs of 

 eyes were on the alert, but a single tuft of verdure 

 visible at a distance could be made out This was 

 formed by several bushes of Prosopis limensis growing 

 together. Elsewhere the few plants seen were con- 

 fined to the occasional shallow depressions where rain 

 rests longest. All, of course, had perennial roots, and 

 scarcely one of them rose as much as three inches 

 from the ground.* 



I found it difficult to account for the origin of the 

 sands which are sparingly scattered over the plateau, 

 but accumulated to a considerable depth on the 

 slopes behind the town. The underlying rock seen 

 in ascending to the plateau is a tolerably compact 

 shale ; but the hard crust forming the superficial stratum 

 appears to consist of different materials, and not to 

 be made up from the disintegrated materials of the 

 shale. At several places, both below the cliffs and 

 on the plateau, I found large scattered fragments of 

 what appeared to be a very recent calcareous forma- 

 tion, largely composed of shells of living species ; but 

 this was nowhere seen in situ, and I was unable to 

 conjecture the origin of these fragments. 



* For a list of the species collected, see \h& Jotirnal of Linnccan Society, 

 vol. xxii. 



