796 



SCIENCE, 



[N. S. Vol. V. No. 125. 



tion of the Arabian sand pits (fulje) of hoof- 

 print form. Some of these described by 

 Blunt are over 200 feet deep, revealing the 

 hard floor on which the loose sand lies. The 

 horns of the crescentic medanos point in the 

 direction of wind motion, because, being 

 lower than the middle, they travel for- 

 ward faster, and thus run ahead of the 

 larger mass. The extension of coast dunes 

 in ridges transverse to the active winds is 

 shown to depend more on the location of 

 the sand supply (the beach) than on wind 

 intention or 'sand tactics.' The longi- 

 tudinal dunes of the Indian desert, parallel 

 to the dominating wind, exhibit the more 

 perfect mastery of the wind over the sand ; 

 they are best developed where the wind 

 is strongest. Transverse dunes are com- 

 pared to large ripples of sand and exhibit 

 the relative mastery of the sand over the 

 wind. The most effective way to check the 

 encroachments of blown sands is to pro- 

 mote the growth of existing dunes by wattle 

 fencing ; thus the advance of individual 

 dunes and the formation of new dunes to 

 leeward are retarded. 



PHILIPPSON ON GEOMOEPHOLOGT. 



Db. a. Philippson, of Bonn, has con- 

 tributed a series of articles to Hettner's 

 Geographische Zeitschrift (ii., 1896, 512-527, 

 657-576, 626-639, 688-703), on the prog- 

 ress of the above subject, in which he recog- 

 nizes two divisions: a dynamical chapter, 

 concerned with the forces at work on the 

 surface ; and a systematic chapter, con- 

 cerned with the classification of forms ac- 

 cording to their characteristic features and 

 their causes. Geological structure and 

 stage of development (by which young, 

 mature and old forms are distinguished) 

 are not given prominent place. Attention 

 is devoted chiefly to the processes by which 

 form is determined ; weathering, transpor- 

 tation by streams, snow, ice, and wind, and 

 the action of the sea, are considered in some 



detail, with numerous references to special 

 articles ; geomorphogeny, rather than geo- 

 morphology, being the leading theme. For 

 example, under transportation by gravity, 

 the determining conditions of landslips are 

 briefly stated, but entirely apart from the 

 structures and the stages of development in 

 which landslips are characteristic and with 

 little attention to the forms that they as- 

 sume. While rational from the point of 

 view of process, such a method seems em- 

 pirical from point of view of form and, as 

 such, characteristic of the current German 

 method of study. 



THOEODSSEN ON NOETHEAST ICELAND. 



K. Keilhack gives an abstract in Peter- 

 mann's Mitteilungen (xLii.,1896, 269-275) 

 of Thorodssen's observations in northeast- 

 ern Iceland in 1895. The Jokulsa delta 

 formerly had a larger population, but is now 

 in part laid waste by the gravels of its ag- 

 grading distributaries. South of the delta 

 flat lava floods of great area spread around 

 cones of moderate height; the lavas are 

 seen to rest on glaciated dolerite. Indeed, aU 

 northeast Iceland bears marks of glaciation 

 where not covered by younger lava flows 

 and ashes. Fissures are noted at various 

 points. East of the Jokulsa delta the 

 broken ground is dislocated on the fissures. 

 Lava flows issue from some fissures, and 

 small craters are built over them. West of 

 the delta fissures were formed during the 

 earthquake of January 25, 1885, with small 

 displacement of adjacent land blocks. The 

 younger lava and tuffs of this region, both 

 pre- and post-glacial, continue southward 

 to the Vatna Jokull, apparently occupying 

 a depressed district between the older ba- 

 salts to the east and west. 



VOLCANIC PHENOMENA OF 1894. 



E. KuDOLPH, of Strassburg, continues the 

 annual report on volcanic phenomena, pre- 

 viously prepared by Kniittel (Tschermak's 

 Min. u. Pet. Mitth., xvi., 1896, 365-464). 



