138 



POND COMMUNITIES 



is characterized by a series of ridges running parallel with the shores of 

 the lake. Their average width is about 30 meters (100 ft.), and they are 

 separated by ponds somewhat narrower. Most of the ponds are several 

 miles long and vary in depth, during the spring high water, from a few 

 inches to 4 or 5 ft. Originally there were probably a number of outlets 

 to the ponds, either connecting them with the lake or with the Calumet 

 River. This river flows across the long ponds at a small angle. The 

 ponds and ridges were formed under water, and the river has cut its 

 way across them with the falling of the lake level. The building of 

 sewers associated with the growth of the Northern Indiana towns has 

 drained a number of the ponds, and roads and railroads have isolated 

 parts of others. 



I. ORIGIN OP THE PONDS (62) 



The waters of the lake appear to have fallen gradually from the 12 -ft. 

 level referred to on p. 47. There are at present usually two or three 

 depressions along the shore of the lake under the water. The present 

 submerged depressions and ridges appear to be strictly comparable 

 to those found on the plain of Lake Chicago, and the ones with which 

 we have to deal probably belong to a series formed by the continuous 

 recession of the lake level (Fig. 83). This gives us a series of ponds 

 differing principally in age, the oldest being farthest from, and the 

 youngest nearest to, the lake. 



As has been stated, the ponds have been partly drained, so that we 

 have been obliged to study isolated portions. The younger members 

 of the series (ist, 5th, yth, and i4th, as counted from the lake) show the 

 greatest differences and have, accordingly, been studied in detail. The 

 arrangement of these ponds is shown in Fig. 83. In addition to the 

 ponds named, the i3th, the $2d, the Q3d, and the 95th have been 

 studied, but with less care. 



2. PHYSICAL CHARACTERISTICS (112) 



The main facts of the topography of the isolated portions studied 

 are shown in Table XX Via. 



TABLE XXVIa 



