DEPARTMENT OF BOTANICAL RESEARCH. 91 



distinctly marked, and there are doubtful signs of several intermediate 

 and lower ones. Doubtless these were produced by temporary pauses 

 in the recession of the lake. 



The channel of the ancient overflow over the Silver Lake divide is 

 clearly marked in the alluvium north of the divide, but is small. In 

 places it is less than 20 feet wide and only 8 to 12 feet deep. Since it is 

 cut in poorly consolidated alluvium and since its grade is ample for 

 extensive alluvial cutting, it is impossible to escape the conclusion that 

 the overflow out of the ancient lake was both small and transient. 

 This is confinned by the entire absence, so far as discovered, of any 

 sign of stream erosion of the rock portion of the divide. No signs of any 

 alternative overflow channel were discovered, in spite of careful search, 

 and the topography renders it improbable that any such channel exists. 



The ancient lake was the sole discharge-point of the ancient Mohave 

 River, and the lake-level must have served as a gage of the river's 

 volume. The fact that the overflow from this lake was so small and 

 transient serves to confinn the conclusions, for which much other 

 evidence is accumulating, that the geologically recent period of lake 

 and river expansion in the North American deserts was neither so 

 humid nor so long-continued as has usually been imagined. It is 

 probable that during most of its existence the Mohave River has not 

 differed greatly from its present character. A period during which it 

 was similar to rivers of the humid regions is not to be thought of. All 

 evidence, however, indicates the reality of the minor climatic pulsa- 

 tions, the existence and importance of which has been emphasized by 

 Huntington. 



Underground Structure andArtesiaii Water in the Desert Valleys of the Great Basin, 



by E. E. Free. 



An incident of the investigations of desert geology and topography 

 during the last ten years has been the accumulation of several hundred 

 records of wells bored in the desert alluvium in search of water or for 

 other practical purposes. Among these are the records of 15 deep 

 holes (500 to 1,200 feet) and over 50 shallower ones which were drilled 

 under my direction. Consideration of this accumulated data, as well 

 as of the physiographic processes now observed to be active on the 

 present surface of the deserts, has led to some generalizations regarding 

 the structure of the underground portions of the desert alluvium, 

 which generalizations are of interest especially in connection with the 

 occurrence of artesian waters in the desert valleys. Such artesian 

 waters have been found in several valleys and under circumstances 

 which indicate considerable differences from the conditions existing in 

 the older artesian areas. 



It is necessary to recall the geographic character of the Great Basin 

 as composed of a series of long mountain ranges separated by long and 



