PHYSICAL FEATURES. ?I 



"way and the results caused by moving ice. Examples of this rock 

 sculpturing may be seen on the crests of any of the rocky hills in 

 Marwar exposed to the prevailing winds, and especially clearly on 

 the smooth surfaces of the glassy Malani lavas (PI. I, fig. i) The pro- 

 cess, in the case of the more highly porphyritic lavas, is assisted by 

 the decomposition and weathering out of the felspars, whereby a 

 pitted surface, giving the rock a vesicular aspect, is formed, affording 

 the sand blast a continually renewed, roughened surface to work on. 



The undercutting and polishing of isolated masses of granite is 

 another instance of the effects of deflation (PI I, fig. 2), and the large 

 hollows frequently seen in the cliffs of granite and lava maybe partly due 

 to the same cause ; but these hollows probably owe their origin more to 

 the weathering out of concretionary masses in the case of the granite, 

 or, in the case of the lavas, to the presence of large gas pores. In both 

 cases the hollows are probably only enlarged and polished by the 

 wind. The hard bands of sub-recent conglomerate often found in the 

 river beds are sometimes affected in a curious way. Where they rest 

 upon softer sands the latter are cut away from under them by the 

 wind, leaving oblong masses of the conglomerate, which are frequently 

 tumbled about at all angles (PL I, fig. 3). If these masses were sub- 

 sequently covered up with silt or sand and the whole consolidated and 

 afterwards denuded, the geologist of the future might have some diffi- 

 culty in understanding how such large masses of apparently transported 

 conglomerate came to be heaped together in a bed of sandy silt, and if 

 he were a glacialist, might be strongly tempted to call them erratics, 

 and ascribe their position to the agency of floating ice or glaciers ! 



Acting as they do on rocks of varied composition and texture, 

 these agents of denudation produce results of very different appear- 

 ance. The highly inclined schists and quartzites of the Aravalli 

 system are formed into long hog-backed ridges with an equal slope of 

 talus on either side ; the undulating sheets of Malani lava form conical 

 Iiills or long ridges with steeply scarped sides and rugged contours, 



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