ECOLOGICAL -ITCESSION. 3 



A- \ve have already -idled, the ponds which ha\'c been -tudied 

 e-pecially, are part- of the long sloughs which have been long 

 enough i-olated to ~ho\\ ihcir efficiency in -upporiing the fi-he- 

 which tlu-v now contain. The ti-hes found in tin- -eparated 

 pond- are-ho\\n in Table XXI. ' p. 171 of the pre-ent paper. 



With the kno\\n habits of fre-h-water fi-he- as a ^uide. the 

 pond- h.i\e lu-en roughly mea-ured and area determined, depth 

 and angle of til- -lope of sides mea-ured. the character of bottom 

 determined, -ketr'n.-d, and the area- of the different kind- e-g- 

 niated on the ba-i- of the sketch--, and the di olved -olid- and 

 lie \\aier- have been determined by chemi-t-. The 

 plant and animal content of the pond- ha- been anab /ed <|tialila- 



ti\el\ and e-timated quantitatively. 



Tlie-e re-nlt- \\ill be |resenled under the main head- of. i 

 l'h\ -ii-al < har.t. Biological Content. 



1. I'liy^iull ('h>: -(a) Topo-r.iphy. The chief topo- 



phii features are -ho\\n in Table I. 



TAHLK 1. 



-IK .\\ i DEPTH AND ^ 



The figure- repre-enting depth ol water are the re-nlt- of 

 me.i-nn-meiit . \\ith e-timatioii in th- -\ averages. \ T 



re-nlt- o| r..ii-li mea-iiring by ] lonntin- rail- in |iarallel 



railroad-, etc. \\liile p^itioii- -tnditd dit'ler in -i/e, the\ pi. -i nt 

 Considerable nnifo|-mit\ of other feature-. 



I llal.H 'lei' .-I Mottoill. The bottom i- ( onipn-rd of pure 



sand, or sand more or less mixed with or deeply covered by humus. 



The -and or tin- In mm- ha- a con -id era Me mi\i nre of marl at -ome 

 point- in the \oim^er pond-. Vegetation iuarl\ al\\a\- covers a 



pure humus bottom. (.'lm><i -m<l bnlrn-1^ netimes gro^ on 



-and and marl bottom-, but in -uch i ases the\ are -i altered and 

 in the table -uch area- are included \\ith bare sand, because -uch 

 sparse vegetation does nol intei tfre \\ ith the breeding of tish. 



