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 OF 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 (1st, 5th, 7th, and 14th, 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 13th, the 52d, the 93d, and the g5th 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 XXVIa. 
TABLE XXVIa 
Pond Area in Sq. M. |Depth in Meters} Average Depth Slope 3-7° Slope 20° 
ite GOO Gale 3,500 0.6 | 0.3 | Much Little 
ieee teh cG.o:64 3,500 °.9 0.5 Less Much 
TO OA 25,000 0.9 0.5 Very little | Much 
i Reieceel aerate 10,000 0.667 0.4 Very little | All 
LObomocsauos 50,000 0.5 0.2 Very little | All 
Bie veteshetale aes 630 0.4 | o.1 Very little | All 
