66 The Control of Mosquitoes 



are present, sharp changes of grade, such as steep 

 hillsides terminating on flat ground, or on more 

 gentle slopes, should be carefully examined. 

 The seepage on a hillside outcrop may approxi- 

 mately follow a contoxir line. The escaping 

 water then flows downhill, and may again be 

 absorbed by the soil, or continue to flow until it 

 reaches a natural drainage course, or come to rest 

 in a depression and form a pool or pond. On hill- 

 side seepage areas only a thin film of water is 

 present, but small depressions in the grotmd give 

 a depth of water sufficient for mosquito develop- 

 ment. 



Naturally the temperature of the water is 

 relatively high and frequently seepage areas con- 

 tain much algae and few enemies of larvae. Cattle 

 complicate the situation by leaving deep hoof- 

 prints. The outcropping water may be present 

 throughout the year or only during short periods. 

 Each outcrop is a law unto itself. Strange as it 

 may seem, some places produce more water 

 immediately after the rainy season, than during it. 

 One such area was discovered at Balboa at the 

 foot of a hill composed largely of trap rock. 



In several localities seepage outcrops had been 

 present only twice in ten years. Of course if 

 such places are neglected it will be extremely 



