258 General Notes. [March, 



three to seventy-one metres annually. The retreat or advance of 

 a glacier depends "on changes of long periodicity in meteorological 

 conditions— heat, moisture, winds." In the Am. Journal of Sci- 

 ence Dr. R. W. Coppinger has some interesting observations upon 

 the movement of the soil-cap on the shores of Western Patagonia. 

 Evergreen forests and brushwood cover the shore hills to a height 

 of one thousand feet, and gravitation, acting on this mass of vege- 

 tation and the soil beneath, resting on a surface already planed by 

 ice-action, causes the whole to slide downward to the water, which 

 removes its free edge in much the same way that the end of a 



Greenland glacier is removed. The Report on the Geological 



and Natural History Survey of Minnesota, for 1880, contains a 

 descriptive list of rocks, descriptions of three new Lower Silurian 

 Brachiopods, and a note on the Cupriferous series by Professor 

 Winchell ; also an account of the Glacial phenomena of the State 

 and the district north and west of it, by Warren Upham. 

 GEOGRAPHY AND TRAVELS. 1 



Dr. Lenz on the Sahara. — Dr. Oscar Lenz gives in the last 

 number of the Zettsckrift of the Berlin Geographical Society 2 an 

 account of the results of his journey across the Sahara, from Tan- 

 ger to Timbuktu, and thence to Senegambia. The following good 

 abridgement of his paper we take from the Nature : 



" The real journey was begun at Marrakesh, at the northern 

 foot of the Atlas mountains, where Dr. Lenz laid in his store 

 of provisions and changed his name and dress, traveling 

 further under the disguise of a Turkish military surgeon. He 

 crossed the Atlas and the Anti-Atlas in a south-western direc- 

 tion. The Atlas consists, first, of a series of low hills belonging 

 to the Tertiary and Cretaceous formations, then of a wide plateau 

 of red sandstone, probably Triassic, and of the chief range, which 

 consists of clay-slates with extensive iron ores. The pass of Bi- 

 banan is 1250 metres above the sea-level, and it is surrounded 

 with peaks about 4000 metres high, whilst the Wad Sus valley at 

 its foot is but 150 metres above the sea. The Anti-Atlas consists 

 of Palaeozoic strata. On May 5, 1880, Dr. Lenz reached Tenduf, 

 a small town founded some thirty years ago, and promising to 

 acquire great importance as a station for caravans. The northern 

 part of the Sahara is a plateau 400 metres high, consisting of hori- 

 zontal Devonian strata which contain numerous fossils. On May 

 15 Dr. Lenz crossed the moving sand-dunes of Igidi, a wide tract 

 where he observed the interesting phenomenon of musical sand, 

 a sound like that of a trumpet being produced by the friction of 

 the small grains of quartz. But amidst these moving dunes it is 

 1 Edited by ELLIS H. Yarnall, Philadelphia. 



•I 



94, 95. P- 2 72. It is accompanied by a large m,;, ol his route. Scale I : 1,500,000. ' 



