25 
No. 1. An open drain through town, known as the 17th St. ditch. 
This ditch is fed quite largely by waste water from the mines supplement- 
ed by small tributaries which carry off the rains and natural surface 
water. 
No. 2 (Fig. 1). Sink-holes to be found in the west part of Herrin, 
the formation of which has already been described. 
Fic. 1. Sink-hole, West Herrin; produces very few mosquitoes. 
-— ~~ 
Fic 2. Woodland pool, north edge of Herrin; a prolific breeder of 
malarial mosquitoes 
