64 PROCEEDINGS OF THE PHILADELPHIA MEETING 



railways are often found to be roughened and etched by continuous impinging 

 sands. Short lengths of steel rail set for clearance posts in similar situations 

 are frequently distinctly girdled just above the ground and brightly polished. 



In the arid regions of Arizona and New Mexico telegrapli wires and electric 

 ti-ansmi.ssion cables are kept bright by the blown dusts. As noted by J. Walther, 

 the telegraph wires of the Trans-Caspian railways have to be replaced about 

 evei-y decade because of the driven-sand action, which in that time reduces the 

 size of the wires to one-fourth of the original. Railway service on the Sahara 

 and other deserts meets with great obstacles due to the frequent terrific sand- 

 storms. One of these difficulties is sought to be overcome by the replacement 

 by spoked wheels of all solid wheels, because the latter under the incessant 

 sand-blast are found to wear so thin within a year's time as to be unfit for 

 further use. 



The destructive effects of blown sands on buildings is noted by many ob- 

 servers. Wind corrasion of Heidelberg castle is often referred to. Injury to 

 building stones in cities by blown sand is especially discussed by T. Egleston, 

 who also calls attention to the fact of the gradual effacement of inscriptions 

 on city tombstones by dust blown from the street. The great obelisk at Heli- 

 opolis, near Cairo, displays blown dust or sand effects by the complete oblitera- 

 tion of the deeply cut hieroglyphics on the south and west faces — the sides 

 directed toward the prevailing winds off the Libyan Desert. Many Egyptian 

 monuments are, according to W. M. F. Petrie, badly injured by abrasion due 

 to wind-driven sands. 



From a strictly geological angle the experimental aspects of sand-blast action 

 are especially considered in a number of recently published papers. My own 

 experiments were undertaken more for the purpose of establishing a rate of 

 abrasion than of merely establishing the fact. Bottles, panes of glass, and 

 rocks were exposed in situations where strong winds were driving the desert 

 sands over the surface of the ground. One wine bottle planted in the soil, 

 with top and bottom protected by cloth and an inch-wide band left in the 

 middle, was forgotten for nearly two years. Chancing to come across it at the 

 end of that period, it was found that the exposed band was entirely etched 

 through the glass for a distance of one-third of the circumference of the bottle. 

 I'anes of glass covered with paraffine figures presented ground surfaces, wher- 

 ever the wax was absent, that were distinctly visible after single severe sand- 

 storms. Hard, homogeneous and fine-grained rock faces were quickly polished, 

 while coarse-gi'ained granitic rocks were unevenly etched, the quartz grains 

 standing out in bold relief. 



From the consideration of the local phenomena as mentioned, and the pro- 

 duction of faceted pebbles, sapped bounders, undermined cliffs, and the accen- 

 tuations of geologic structures, passage is made to some of the broader aspects 

 of the formation by the same means of the positive features of relief which 

 characterize desert regions — the production of cliff-lines, the origin of canyon 

 reentrants, the growth of desert escarpments, the genesis of plateau plains, 

 and the girdling of the desert ranges. 



The rate of general sand-blast corrasion in arid lands is regarded as more 

 rapid than that of general stream corrasion in humid countries. In addition, 

 there are to be taken into account, in the consideration of the regional degra- 

 dation of desert tracts, both the effects of insulation and of deflation. 



Presented by title in the absence of the author. 



