June, 1919] 



Fauna of Rock Bottom Ponds 



461 



Each of the three ponds was examined but attention was 

 centered on the lower one. If there has been faunal contam- 

 ination, so to speak, from the creek this pond would have been 

 most effected, although once a form had migrated along the 

 ditch to this point it could have gone on to the two upper ponds. 

 The natural sequence of physical changes has apparently been 

 least interfered with by man in the lower pond. Except for 

 some masonry at one end to build a bridge and at the other to 

 make an outlet, the conditions have taken a natural course. 



A portion of the Thirty Year Pond. 



The pond has an area of eighty by eighty-five feet. A 

 portion of it is shown above. Its edges were still littered 

 with the fragments of stone common about a quarry. Above 

 these was a lawn and trees. The water was two to four feet 

 deep, although this depth may vary as much as a foot from 

 year to year. I have never seen it overflowing into the ditch. 

 Its temperature was 29° C. The surface of the water has 

 usually been well covered with Lemna. Beneath this, and dis- 

 tributed rather generally, there were filamentous algse. From 

 four inches to a foot of rich, black sediment, largely composed 

 of decayed vegetation, covered the bottom. In this at several 

 spots the pond lily, Castalia tuberosa, had taken root. Sticks 

 and small branches were scattered about promiscuously. Along 

 the edges there was a miscellaneous litter of leaves, sticks and 



