276 ANNUAL OF SCIENTIFIC DISCOVERY. 



and larger portion of the Sahara, we have similar reports from the natives 

 of mountain chains and lofty highlands; as, for instance, of the Black 

 Mountains, which extend from the coast far to the inland, and of a moun- 

 tain chain fringed on its eastern border by several oases, that of Tuat among 

 the rest: but especially renowned is the frowning Haghar group, with its 

 three or four sheer, steep, and dizzy walls of rock, each wall 125 miles in 

 length; this is said to be surrounded by an immeasurable sea of sand, and 

 to form the stronghold of the most powerful and the most predatory of all 

 the Tuareg tribes, that of the Haghar Tuareg, who, amid these high moun- 

 tain fortresses, are compelled to go clad in woollen and furs. 



And yet there remains, as well in the northern part of the Sahara as in 

 much of its western portion, room enough for vast patches of sand or salt 

 deserts, among which, according to the accounts of the natives, Tanezruft, 

 lying on the route between Tuat and Timbuctoo, is the most remarkable in 

 extent; and it may be a question whether a scientific exploration will not 

 reveal the existence of the plateau formation at least in some portions also 

 of this desert. 



In regard to plants and animals, we find that the necessary conditions of 

 their existence, namely, rain, is by no means so rare a phenomenon as our 

 earlier accounts have led us to conclude. For, though Sahara may perhaps 

 justly continue to be regarded as in the main a rainless belt, yet we find 

 many exceptions in sudden and very copious showers, and it is altogether 

 likely that there are many tracts, like the oasis of Air, which have their 

 regular rainy seasons; for we find, even in the northern Hamadah, scattered 

 thickets and a few small birds. SiUiman's Journal. 



MEASUREMENTS OF THE ALLEGHANY SYSTEM. 



It is well known to the scientific men of this country that Professor 

 Arnold Guyot, of Princeton, New Jersey, has devoted a portion of his 

 summer vacations for ten years past to the study of the different portions of 

 the great Alleghany s} r stem which faces the Atlantic coast from Canada to 

 Georgia. Several years ago he measured the highest peaks of the Adiron- 

 dack, Green, and White Mountains, in the northern part of the chain, and 

 more recently he has been at work on the southern portion of the system, 

 which is found to possess the most elevated peaks of the whole Appalachian 

 chain. 



By a private letter from Professor Guyot, we learn that during his last 

 summer (1860) he has devoted two full months to further measurements in 

 the south, in company with Messrs. Sandoz and Grand Pierre. The weather 

 has been propitious, and he has accomplished much work, having measured 

 between one hundred and fifty and two hundred points in addition to those 

 which were previously determined. He has extended his investigations 

 as far as Georgia, and has seen the extremity of the Blue Ridge and the 

 Unaka. 



These measurements sufficiently indicate the grand traits of structure of 

 that loftiest portion of the Appalachian system. It may be seen that the 

 Roan and Grandfather mountains are the two great pillars on both sides 

 of the Northgate to the high mountain region of North Carolina, which 

 extend between the two chains of the Blue Ridge on the east and the Iron 

 and Smoky and Unaka mountains on the west. That gate is almost closed 

 by the Big Yellow mountain. The group of the Black Mountain rises nearly 



