56 THE U. S. GEOLOGICAL SURVEY 



serve as a breeding place for Anopheles, the mosquito to which 

 malarial infection is due. 



Altogether the Survey has accumulated a vast amount of 

 accurate data of both scientific and economic value on the 

 ground waters of the United States. A total of 474 papers 

 has been published relating in some way to ground water, of 

 which 271 papers relate primarily to this subject. Many of 

 these papers include detailed maps showing the ground-water 

 conditions in specific areas. In addition to the data already 

 published there is a great quantity on file at the Geological 

 Survey still unpublished. 



About 75 per cent of the area of the United States (exclud- 

 ing Alaska and the Insular Territories) has been covered by 

 ground-water surveys of some sort, and about 25 per cent 

 has been covered by what may be called standard ground- 

 water surveys. The total area covered by intensive surveys 

 is very small, amounting to only a fraction of 1 per cent of 

 the total area of the United States. 



The Survey for some years has published in its water supply 

 papers notes on desert watering places, but in 19 17 a specific 

 appropriation of $10,000 was granted by Congress "for dis- 

 covering, developing, protecting, and rendering more access- 

 ible, springs, streams, and water holes on arid public lands of 

 the United States; for erecting and maintaining suitable and 

 durable monuments and sign-boards; and for providing con- 

 venient and ready means, apparatus, and appliances by which 

 water may be brought to the earth's surface." The Survey 

 has devoted the funds thus appropriated to prosecuting more 

 vigorously than has hitherto been possible the survey of water- 

 ing places, and to preparing guides and maps, and erecting 

 sign-posts directing to them. 



The total area sufficiently arid to require maps and guides 

 to desert watering places is about 570,000 square miles, or 

 nearly one-fifth of the area of the United States, exclusive of 

 Alaska and the Insular Territories. Of this area about 

 75,000 square miles have been surveyed since July 1, 1917, 



