306 



SCIENCE. 



[N. S. Vol. XXIII. No. 582. 



placer miners. In collecting samples it is 

 especially necessary that the amount of gravel 

 represented by the concentrates should be 

 noted. 



The following papers were then presented: 



Geological Beconnoissance Map of Alasha: 



Mr. Alfred H. Brooks. 

 Gypsum Beds and Water Storage in the Pecos 



Valley of New Mexico: Mr. Willis T. Lee. 



An irrigation system has been in operation 

 for eleven years in the Pecos Valley near 

 Carlsbad, N. M. The storage reservoir of the 

 system at McMillan began to lose water by 

 underground leakage soon after its comple- 

 tion, and this loss became progressively more 

 serious until at the present time the reservoir 

 is almost useless. This paper deals with the 

 geological conditions which have resulted in 

 the leakage of the reservoir and possible 

 remedies are being investigated by the rec- 

 lamation service. 



The rock f omiations are the ' red beds ' of 

 the plains which in this region contain strata 

 of gypsum to a depth of 1,500 feet. Rock salt 

 occurs in large amounts near Carlsbad and 

 the distribution of salt springs indicate that 

 it may have formerly extended throughout the 

 Carlsbad region. Sink holes exist wherever 

 the gypsum occurs near the surface in the 

 vicinity of the river. These sinks connect 

 with caverns formed by solution of the gyp- 

 sum beds and they are numerous enough to 

 warrant the assumption of a general honey- 

 combed condition throughout the gypsiferous 

 formation. Removal of the soluble strata and 

 the falling in of the caverns produced must 

 undoubtedly have permitted a gradual depres- 

 sion of the surface of the ground, and it is 

 suggested that this process has been the effect- 

 ive cause in producing the basins in the valley 

 near Carlsbad. This hypothesis has been ap- 

 plied by Mr. C. A. Fisher, of the United 

 States Geological Survey, to account for the 

 origin of the Roswell Basin north of Carlsbad, 

 where the fractured and insoluble mass of 

 residual strata is reported to be more than 

 1,000 feet in depth. In the Carlsbad region 

 details have not been worked out, but the in- 

 soluble strata are undoubtedly in a fractured 



condition, allowing free circulation of water 

 under ground. In part, at least, the water 

 which runs into the ground at the McMillan 

 reservoir returns to the surface above Carls- 

 bad. In the case of one large spring below 

 the dam the rate of flow depends upon the 

 height of water in the reservoir, but it is by 

 no means certain that the supply of this 

 spring is entirely leakage from the reservoir. 



Glacial Phenomena in the San Juan Moun- 

 tains: Mr. Ernest Howe. 

 In addition to the drift that has long been 

 recognized in the San Juan Mountains, cer- 

 tain detritus has been observed at various 

 places that is evidently older, but in regard to 

 the origin of which information has hitherto 

 been lacking. Quite recently evidence has 

 been found in the IJncompahgre Valley which 

 suggests that certain of these deposits may be 

 of glacial origin. 



The events of the later stage of glaciation 

 are recorded in a slight but characteristic 

 modification of the topography, and in an 

 abundance of drift in the form of moraines 

 and outwash gravels, oxidized but little, and 

 upon which subsequent erosion has had slight 

 effect. Post-glacial erosion has been insig- 

 nificant in the higher mountains, and it is 

 believed that glacial conditions continued to 

 exist until comparatively recent times. 



The older detritus occurs farther from the 

 mountains than the more recent material and 

 rests upon the remnants of an old topography 

 that was deeply dissected prior to the last 

 stage of glaciation. The form of the deposits 

 suggests that they have undergone much modi- 

 fication, and the materials composing them 

 have been more or less decomposed by atmos- 

 pheric agents. The evident greater age of 

 this detritus is in strong contrast to that of 

 the drift deposited by the last glacial ice. The 

 large size of individual boulders, the hetero- 

 geneous character of the material and the 

 distance from its source suggest transporta- 

 tion and deposition by glaciers as an explana- 

 tion of the origin of these deposits. 



Stratified deposits of water-worn gravels, 

 closely related to the older drift in age and 

 position, extend far out from the mountains 



