752 



SCIENCE 



[N. S. Vol. XXIX. No. 749 



A topographic map dravm from original surveys 

 of the gorge of this, the Mills glacier, and the 

 moraines which it built, has been prepared. 

 The Bed Beds of the Wichita-Brazos Region of 

 Worth Texas:' C. H. Goedon. 

 The region to which this paper relates is of 

 special interest as having furnished the data for 

 the discussions on the Texas Permian which have 

 appeared in various publications in recent years. 

 In the study of the underground water conditions 

 of the region under the auspices of the U. S. 

 Geological Survey, it was observed that the red 

 sandy shales and red sandstones so conspicuous 

 in the Wichita valley region were replaced south- 

 ward in large part by blue shales, light-colored 

 sandstones and limestones. In some places the 

 transition from a sandstone into a limestone was 

 plainly seen. Formations to which the names 

 Wichita and Clear Fork have been given, when 

 traced along their strike toward the southwest, 

 are found to grade into those included under the 

 terms Cisco and Albany. The former have been 

 regarded as Permian, while the latter have usually 

 been assigned to the Pennsylvanian. Some authors, 

 however, have suggested that the Albany should 

 be considered Permo-Carboniferous. An abundant 

 marine fauna characterizes the beds toward the 

 south. In the Red Bed region marine forms are 

 few, appearing only in the few beds of limestone 

 that persist. Along with them in this region 

 appear vertebrate remains upon which the refer- 

 ences to the Permian have been based. It is the 

 conclusion of the author that the Red Beds of 

 this region are the near-shore representatives of 

 the Albany and the decision as to their age will 

 rest upon that of the latter. 



The Invertebrate Faunas and Correlation of Some 

 So-called Permian Kocks of the Mississippi 

 Valley, with Remarks on Their Stratigraphy: 

 J. W. Beede. 



Discussion of the stratigraphy, fossils and cor- 

 relation of the higher Paleozoic rocks of Kansas 

 and Nebraska and their correlation with rocks of 

 the United States and Eurasia. Remarks on 

 stratigraphy and paleophysiographic conditions 

 under which faunas lived, and a few fundamentals 

 of paleontologic correlation. 



Differential Effects of Eolian Erosion upon Rock- 

 belts of Varying Induration: Chables R. Keyes. 

 The desert regions of our country may be re- 

 garded as comprising those tracts where the an- 

 nual amount of rainfall is less than ten inches. 

 " Published by permission of the director of the 

 United States Geological Survey. 



More than nine tenths of whatever rainfall there 

 is sinks at once into the dry and thirsty soil and 

 does not appear as stream-water at all. The only 

 perennial rivers are those whose headwaters are 

 extralimital and whose courses merely traverse 

 the arid region on the way to the sea. With so 

 small and unimportant precipitation character- 

 istic of the arid country, the high evaporation, 

 often several times greater than the amount of 

 annual rainfall, and the loose dry soils, wind- 

 scour becomes a far more potent erosive agency 

 than is usually fancied. 



The sequence of geologic terranes and their 

 lithologic characters in the desert region, and 

 particularly in the northern part of the Mexican 

 tableland where the isle-like aspects of the moun- 

 tain ranges dotting a vast sea of earth is so char- 

 acteristic of what the Germans in the South 

 African deserts have so aptly termed the "Insel- 

 berglandschaft," are such as to permit eolian in- 

 fluences to fashion their finest subjects of desiccate 

 sculpture. Ten thousand feet of hard limestones 

 are succeeded by an even greater thickness of soft 

 shales and friable sandstones. On account of fre- 

 quent and profound faulting which, in early Ter- 

 tiary times, the region had undergone and the 

 subsequent planing off of the country to the con- 

 dition of a peneplain, there has been imparted to 

 the areal distribution of the geologic formations 

 a remarkable alternation of belts of resistant and 

 weak rocks. 



General desert-leveling and lowering of an ele- 

 vated country by deflation is comparable in the 

 nature of its larger relief effects to that of general 

 corrasion in a humid climate. It is in the arid 

 region that the eolian influences as erosional 

 processes find their maximum activities. In the 

 dry lands the weaker rock-masses are rapidly 

 removed; while the harder belts long resist dc- 

 flative attack. Under conditions of aridity, the 

 differential effects of wind-scour, or deflation, 

 upon rock-belts of contrasted induration are very 

 different from what they are in a normal moist 

 climate. The inequalities of surface relief are in 

 consequence very much more intensified than when 

 stream-action is the chief eroding agent. In gen- 

 eral, it may be estimated that in the case of hard 

 rock-masses in an arid land deflative erosion is 

 probably less than one tenth as efficient as in a 

 normal wet country water-action would be; while 

 in the case of weak rocks it is more than ten 

 times greater. This is, no doubt, one of the prin- 

 cipal reasons why to most observers in the desert 

 regions such manifest evidences of enormous ero- 



