April 6, 1917] 



SCIENCE 



335 



Dr. Charles A. Mann, of the University of 

 Wisconsin, has been appointed associate pro- 

 fessor of chemical engineering at Iowa State 

 College, to succeed Professor George A. Ga- 

 briel, who has resigned to undertake industrial 

 work. 



At Tale University Samuel James Record, 

 at present an assistant professor in the For- 

 estry School, has been elected professor of for- 

 est products, and Assistant Professor Ralph 

 Chipman Hawley has been promoted to a full 

 professorship of forestry. 



Howard Lilienthal, M.D., (Harvard, '87), 

 has been appointed professor of clinical sur- 

 gery in the Cornell University Medical School. 



Me. E. D. Merrill, botanist in the Bureau 

 of Science, Manila, and for the last four years 

 associate professor of botany in the University 

 of the Philippines and head of the department, 

 has been promoted to the full professorship. 

 His services will be divided between the uni- 

 versity and the Bureau of Science as in the 

 past. 



The resignation of Dr. E. A. Letts from the 

 chair of chemistry in the Queen's University, 

 Belfast, is announced. 



DISCUSSION AND CORRESPONDENCE 



EPICENE PROFILES IN DESERT LANDS 



In the genetic analysis of the land forms 

 characteristic of arid regions there seems to 

 be an inexplicable proneness to derive all relief 

 effects not through means of the mastering 

 erosive powers peculiarly dependent upon 

 aridity but through the operation of the same 

 geologic processes which produce the land- 

 scape features under conditions of normal 

 humid climate. This far too general tendency 

 to regard all geographic agencies as differing 

 merely in degree and not in kind inevitably 

 leads to erroneous conclusions concerning the 

 origin of many relief details. Although in the 

 instance of desert lands there are not only 

 more but different erosional agencies to be 

 taken into account there is actually less com- 

 plexity involved than in moist lands. On the 

 other hand while there is still the simulta- 

 neous working of several distinct processes a 



little-known one becomes dominant and so 

 thoroughly ascendant as to all but completely 

 obscure the operations of the others. To this 

 aspect of the desert problems little attention 

 has been heretofore devoted. 



Although this exceptional simplicity of land- 

 scape derivation obtains in typically desert 

 tracts it appears to be not nearly so prevalent 

 either on the borders of the desert or in the 

 penumbral semi-arid belts. In the last men- 

 tioned situation there is a notable mingling 

 of relief effects produced by the action of sev- 

 eral distinct erosional processes. Here re- 

 corded observation chances to be most exten- 

 sive and generalization most rampant. Here, 

 too, because of the fact that the examination 

 of the features is attended by strong bias of 

 moist climate experience misinterpretation of 

 true desert characters is rife. 



By inference, at least, use of the title " Epi- 

 cene Profiles " applied to arid tracts, presup- 

 poses the recognition of other relief effects. 

 The erogenic profile which has been so long 

 inseparably associated with desert topography 

 is at once relegated to the back-ground. By 

 its elimination a diametrically opposed prop- 

 osition is substituted for that most brilliant 

 of geological concepts — the fault-block hypoth- 

 esis of basin range structure whereby the 

 mountain prisms are tilting and floating as do 

 ice-cakes in a river at time of spring break-up. 



The early impression that desert ranges, as 

 those of the Great Basin for instance, are bur- 

 ied mountains still strongly persists. But 

 there are many phenomena in such regions 

 that water-action does not begin to explain. 

 The rock-floor which many interment basins 

 display is one of them. The smooth plains 

 surface of enisled landscapes at once excites 

 greatest interest. To find such tracts areas 

 of profound degradation instead of extensive 

 aggradation, as one is led to expect after ac- 

 cepting the water-action hypothesis, is truly 

 surprising. Whether desert tracts of this de- 

 scription owe their facial expression mainly to 

 pre-arid corrasion by streams all traces of 

 which have long since vanished, whether the 

 sloping interment plains are the result of sheet- 

 flood erosion, or, as is still more lately proposed, 

 the rock-floor of desert piedmonts is due to 



