66 



THE NAUTILUS. 



tions in the creek. In October it rose very rapidly, but shortly 

 subsided, and in November, at the time when the entire state 

 was visited by the most severe flood since 1869, it was again 

 subjected to a very thorough scouring. Excessive rains fell on 

 several consecutive, days, and streams in the entire Colorado 

 watershed were out of their banks. 



After the heavy rains of the earlier part of the month there 

 were several days upon which the rainfall, while comparatively 

 light, was sufficient to keep the creek much higher than its 

 normal level. When the water finally subsided to its normal 

 amount the bed was covered completely with a layer of detritus 

 and soft green humus and algae from a half an inch to an inch 

 in thickness. This deposit and the acids formed from it have 

 been the cause of a much more rapid disintegration of the lime- 

 stone than had been the case in the immediately preceding 

 years. Loose pieces of limestone which were exposed to the 

 action of the water had in many cases fallen apart by the end 

 of January. Further rises occurred on April 27 and on May 

 20th, 1914, but were not sufficient to remove all of the accumu- 

 lated layer of detritus. 



In January 1914, a search for snails where they had before 

 been numerous failed to reveal a single specimen of Planorbis 

 and less than half a dozen Physa. Even in the deeper pools 

 they could scarcely be found. Later in the spring in the lowest 

 part of the stream a number of very small Physa, as well as 

 some clusters of eggs were found. The force of the current had 

 been so great as to wash the snails down to the river, and it is 

 possible that the condition of the water due to the decomposing 

 humus may have affected those which were able to escape the 

 flood danger. That some of the Physa were left after the flood 

 may be attributed to their pointed shape which decreases the 

 amount of force that the water was able to exert on them as 

 compared with that on the flat Planorbis shells. Except as 

 noted above in April and May 1914, the conditions in the creek 

 remained as normal. 



In January 1915, Physa has again made its appearance in 

 the middle parts of the stream, although in small numbers only. 

 Diligent search, however, failed to reveal a single Planorbis. 



