244 



D. T. MacDOIJiGAL 



thousand miles to the Atlantic Ocean, has a continental tj^pe of 

 climate in which the only possible precipitation would be that re- 

 sulting from the upward movement of great bodies of heated air 

 resting on land masses of extended area, with consequent inrush 

 of colder air and rain-fall. Months, or even years, msLV intervene 

 between the confluence of conditions which might bring about pre- 

 cipitation in any one place in this desert; which is, therefore, 

 about as arid as any portion of the earth's surface. This is fur- 

 ther indicated by the possible evaporation which might take place 

 from a free water surface, variously measured and estunated as 

 being about twelve to fifteen feet yearlj^ in portions of the Lib- 

 yan desert and the Sahara to the westward ; which is much greater 

 than that of any part of the American desert. 



The Red Sea of the Pharaohs, like its prototype the Red Sea 

 of Cortez (Gulf of California), stretches away to the southeast- 

 ward from the mouth of a river which has traversed a great desert 

 on its way from the mountains to its delta. The mountains in 

 both cases rise with some abruptness from near the western shore. 

 During three days of steaming east of Suez, we saw ranges rising 

 with increasing height until westward of our landing place at Port 

 Sudan, Gebel Erba with an elevation of over five thousand feet was 

 sighted. 



The reddish-brown slopes appeared forbiddingly bare and decep- 

 tively near; but the desert- wise traveler is accustomed to wide 

 spaces on the map, and knows from experience that -the vegetation 

 of regions with certain periodic rainfall will be rich in species of 

 highly localized distribution. A day's experience in these moun- 

 tains near Kamobsana, a week after our landing, afforded an addi- 

 tional illustration of this fact; as sixty species of seed-plants in 

 bloom were collected from a single hill and from the bed of the 

 khor or stream way at its base, in a few hours. 



Sea beaches are much the same ever3'^\^here in the temperate zone 

 by reason of the uniformly saline character of the substratum and 

 the equable temperature; the chief differences in the vegetation 

 being due to the presence of rock, sand, clay or mud deposits 

 above the tide line. 



It seemed highly appropriate that we should begin our westward 



