590 



SCIENCE. 



[N. S. Vol. III. No. 



DETEITAL SLOPES IN AEID REGIONS. 



An excursion into eastern California, in- 

 land from the Sierra Nevada and north of 

 the Mohave desert, is described by H. W. 

 Fairbanks in the American Geologist for Feb- 

 ruary. The chief mountain ranges are held 

 to be uplifted blocks, little dissected ; the 

 form that they had before uplift does not 

 appear to have been considered. The long 

 slopes of coarse detritus reaching forward 

 from the mountain flanks into the desert 

 valleys, constitute characteristic features of 

 the region, as has been pointed out by 

 various observers. Alluvial fans occur with 

 a radius of from six to twelve or fifteen 

 miles. Laterally confluent fans form nearly 

 uniform slopes. A granite ridge south of 

 El Paso range is almost buried in its own 

 waste ; the long marginal slopes of gravel 

 and boulders extend head wards into the 

 shallow canons and reach almost to the 

 ridge summits. Viewed from a distance of 

 ten miles, but little of the granite appears 

 to project above the gravel slopes. 



Following a use of terms that needs re- 

 form, Fairbanks mentions this ridge as an 

 excellent example of baselevelling. But 

 is it not manifest that, even when the heads 

 of the granite mountains are worn down 

 still lower, the general surface of the detrital 

 slopes will continue to suffer slow degrada- 

 tion for a long time ; and furthermore, if 

 the climate of the district had been rainy, 

 is it not true that the existing slopes would 

 not have been assumed. The graded form 

 that the region has almost reached is a 

 function of time and climate as well as of 

 altitude with respect to baselevel. These 

 important topographic controls are neg- 

 lected if the region is said to be baselev- 

 elled. 



THE ICE FALL ON THE GEMMI PASS. 



The ice fall from near the summit of the 

 Altels peak, southeast of the Gemmi pass, on 

 September 11th, last, is now fully mapped, 



figured and described by Heim in a most 

 interesting report made to the Swiss glacier 

 commission (Die Gletscherlawine an der Al- 

 tels, Zurich ISTaturf. Gesellsch. Neujahrsbl. 

 1896.) About four and a half million cubic 

 meters of ice slid down an incline some 

 four kilometers long, descending from 3,200 

 to 1,900 meters above sea level. Gathering 

 about a million cubic meters of rock waste 

 on the way, the gliding mass ran across the 

 valley floor, dashing far up the opposite 

 slope and falling back again, like a wave 

 from a cliff. Finally settling, the debris 

 occupied a square kilometer of surface to 

 an average depth of five meters. A bench 

 on the path of the sliding ice two hundred 

 meters above the valley caused it to spring 

 forward, like a boy's sled passing a ' hump' 

 in his coast, for a time clear from the 

 ground ; then falling, the air beneath it was 

 violently driven out to either side, bearing 

 fragments of ice and stones and overturn- 

 ing trees for several hundred meters later- 

 ally and forwards, and thus nearly doub- 

 ling the area afflicted. As in all Helm's 

 work, the pictures gain great value from 

 being drawn and lithographed by his own 

 hand. One of the photographs represents 

 the genial Zurich professor standing on 

 the ice conglomerate. 



INTEEGLACIAL VALLEYS IN FRANCE. 



Maecellin Botjle has recently made an 

 interesting communication to the French 

 Academy on the older and younger — plio- 

 cene and quaternary — glaciation of Au- 

 vergne (Comptes Eendus, December 2, 

 1895), from which it appears that the val- 

 leys of the elevated plateau of central 

 France were excavated during a nouglacial 

 interval. The upland bears extensive de- 

 posits of morainic material with scratched 

 stones of all sizes and numerous roches 

 moutonnees, implying an extensive glacia- 

 tion. Beneath this upland, valleys are 

 trenched to a depth, two, or even three hun- 



