754 



SCIENCE. 



[N. S. Vol. XI. No. 280. 



aridity of the climate and to the great scarcity 

 of perennial streams, are the " bare, jagged 

 mountains rising out of the plains, ' like islands 

 from the sea,' the abundance of the evidences 

 of volcanic action in times geologically recent, 

 the parallelism of the mountain ranges with 

 one another and with the Pacific coast, the 

 general absence of trees, the preponderance of 

 evergreen vegetation, with its dull, leaden- 

 green hue, the prevalance of thorns in nearly 

 all vegetation, the general absence of fragrance 

 in flowers, * * * and the abundance and large 

 size of the cactus." The trail across the Yuma 

 desert passes numerous graves or monuments 

 to travelers who lost their lives from thirst. 

 Besides the volume of text, with 49 plates, 

 there is an atlas containing an index map, 19 de- 

 tailed maps on scale of 1 : 60,000 with sketched 

 contours, and five plates of profiles, and an al- 

 bum of 258 excellent plates reproduced from 

 photographs of the boundary monuments, and 

 showing, incidentally, an unequalled series of 

 landscapes of that desert region. 



GLACIATION OF SIEEEA COSTA, CALIFORNIA. 



The ' Ancient Alpine glaciers of the Sierra 

 Costa mountains in [northwest] California,' are 

 described by O. H. Hershey (Journ. GeoL, vii, 

 1900, 42-77). The peaks reach 7000 to 9000 

 feet. Non-glaciated valleys are V-shaped, 

 hardly wider at the bottom than their streams, 

 and with ragged spurs projecting from their 

 sides. Where the walls are of serpentine, land 

 slips have occurred, forming hummocky, mor- 

 aine-like masses in the valley bottom. If fol- 

 lowed up to their glaciated stretches, they be- 

 come open U-shaped, with smooth slopes, free 

 from lateral ravines and spurs. Above the 

 smoothed glacial channels, the mountain slopes 

 are still ragged, deeply scored with ravines. 

 Lateral moraines are well developed ; terminal 

 moraines are less distinct. The heads of the 

 main and branch glaciated valleys are clifl'- 

 walled corries, often holding small rock -basin 

 lakes. Meadows of bog and grass occupy por- 

 tions of the upper valley floors, as if replacing 

 shallow lakes. Further down, the trunk val- 

 ley floors are often broken by precipitous steps 

 from one to five hundred feet high. 



A curious case of stream diversion by glacial 



action is described. The upper part of the valley 

 of Coffee creek (descending northeastward) had 

 in preglacial time a higher floor than the neigh- 

 boring upper part of the next valley on the 

 west, that of South fork of Salmon river (de- 

 scending northward), the two being separated 

 by a low dividing ridge. The glacier of Coffee 

 creek obstructed its own valley by a moraine 

 several hundred feet thick, and at the same 

 time ran over a sag in the low lateral divide 

 and descended westward into the adjacent 

 deeper valley, wearing down a gorge through 

 the sag. Hence the present head of the South 

 fork of Salmon river rises in the head of the 

 former Coffee creek valley, follows it for five 

 miles to the valley-floor moraine, within a few 

 hundred yards of the present head of Coffee 

 creek, then turns west through a narrow and 

 rapidly descending cleft and thus deserts the 

 Trinity for the Klamath river system. 



THE TROUGH OF LAKE NYASSA. 



The suggestion made by Thomson in 1882 

 that Lake Nyassa in southeast Africa lies in a 

 down-vaulted trough or Graben is confirmed by 

 Bornhardt {Verhandl. Gesellsch. f. Erdk., Berlin, 

 xxvi, 1899, 437-452). The lake surface is 500 

 meters above sea-level ; its bottom sinks several 

 hundred meters below sea level. On either 

 side are highlands from 1000 to 2000 meters in 

 altitude. Fault breccias occur along the border 

 of the trough. The highlands on the northeast 

 where traversed by Bornhardt, consist in part 

 of gneiss and granite. At a moderate distance 

 back from the rapid descent to the lake, the 

 highland surface presents gentle undulations 

 with broad and shallow valleys of gentle fall, 

 while the border of the highland for 10 or 15 

 kil. back from the trough is trenched by tor- 

 rential streams in deep valleys of rapid fall, 

 and the rolling surface is there transformed 

 into a series of ragged ridges, scored by steep 

 ravines. Here erosion is in its youthful stage ; 

 on the broader highland surface erosion has 

 reached a stage of repose (Buhestand) at the 

 close of a long undisturbed period. The ac- 

 tivity of the young streams in the highland 

 border indicates a geologically recent date for 

 the production of the trough. 



W. M. Davis. 



