August 2, 1907] 



SCIENCE 



153 



metamorpliosed Silurian strata. The Archean 

 area is a smooth platform, a plain of hardly 

 perceptible undulation, its barren surface of 

 bare rock being frightfully desolate; it is in- 

 terrupted by weathered blocks, often standing 

 in fantastic heaps, and by isolated knobs, 

 which gain an exaggerated appearance of 

 height by reason of the extraordinary flatness 

 of the surrounding plain. The areas of erup- 

 tive rocks preserve a greater relief and a more 

 rugged surface; here the trails are at their 

 worst. The Silurian areas possess rounded 

 swells of quartzite between broad shallow de- 

 pressions; that is, old ridges between old val- 

 leys, and thus present a landscape of low, 

 gently modulated forms in contrast with the 

 plain and boulder heaps of the Archean area 

 and with the stronger reliefs of the eruptives. 

 The peneplain as a whole slopes evenly from 

 about 800 m. altitude in the northeast to about 

 600 m. in the southwest in a distance of 200 

 kil. It is spoken of as a block, faulted and up- 

 lifted in mass. Nevertheless its border on the 

 northeast presents only gentle slopes; there 

 alone are the water courses distinctly enclosed 

 in well-defined valleys beneath the upland 

 surface. Elsewhere the drainage system is 

 highly peculiar, and expresses far-advanced 

 old age, the altitude at which the gently in- 

 clined plain now stands being, in the re- 

 viewer's opinion, suggestive rather of the 

 inability of the weak, wet-weather, silt-laden 

 streams as yet to have worn their courses 

 closer to normal baselevel, than of elevation 

 in mass after reduction by normal erosion to 

 a lower level. On the Archean area the val- 

 leys appear to be so old and the interfluves so 

 completely worn down, that the wadies turn 

 about " sur une peneplaine rigoureusement 

 horizontale." In the dry season the wadies are 

 not barren stony beds marked by the work of 

 violent floods, like the wadies of the Sahara 

 farther north, but smooth plains of fine 

 alluvium, more or less overgrown with grass 

 and bushes which survive on the ground water 

 stored from the previous wet season. 



The alluvium of the wadies is not separated 

 from the bare-rock plains by any distinct 

 border or banks, but the surface of one merges 



into that of the other ; towards the wady border 

 the vegetation thins out and disappears. 

 When the short-lived local rains supply water 

 enough to run from the impermeable rock 

 plains, a wady flows not as a stream, but 

 rather as a sheet of very small depth, great 

 breadth (over a kilometer) and feeble current, 

 soon to be absorbed in the silty alluvium — 

 " une nappe d'epaisseur pelliculaire, tres 

 languissament progressive, et bien vite ab- 

 sorbee par I'enorme masse des alluvions." 

 Nowhere else in the world does a single river 

 bear so many names in different parts of its 

 couree. A large scale map would show the 

 drainage system of this peculiar region as 

 abnormally, clumsily broadened. Gautier adds 

 pertinent notes on climate, flora, fauna and 

 inhabitants. W. M. D. 



A PREHISTORIC LANDSLIDE IN THE ALPS 



Deteital hillocks in various Alpine valleys, 

 formerly interpreted as moraines, have in more 

 recent years been recognized as prehistoric, 

 usually postglacial, landslides. One of the 

 best examples of the kind is that by Kander- 

 steg, south of Lake Thun, first identified as a 

 landslide by Briickner in 1891; and lately 

 described in detail by V. Turnau (Inaug. 

 Dissert., Univ. Bern, 1906). The material 

 came from a huge nitch, still clearly defined, 

 on the northwestern side of the Fissistock, 

 where the strata dip down the slope and out- 

 crop in basset edges on the steepened wall of 

 the glacially overdeepened valley of the 

 Kander. The nitch is about three kilo- 

 meters long, and nearly one wide; its upper 

 cliffs reach 3,000 m. altitude; its lower edge 

 lies at 1,500 m. The detritus occupies the 

 Kander valley for a length of 8 kil., northward 

 from the point of its oblique entrance, with a 

 width of from a half to one kilometer, the 

 valley floor at the entrance of the slide being 

 1,200 m., and at its lower end, 800 m. altitude. 

 The highest part of the slide is opposite its 

 source, where the gliding mass was banked up 

 against the opposite valley wall. The thick- 

 ness of the detritus is seen to vary from 150 

 to 30 m., but its bottom is not observed. Its 

 form is extremely irregular, and it has greatly 



