374 
lections determining the direction of the change in production 
are given under the date of the later collection, and the posi- 
tion of the entries also indicates the direction of the change. 
VARIATIONS IN THE MOVEMENT OF PRODUCTION IN DOGFISH AND QUIVER LAKES, 1896. 
Apr. 24] May8 |May 16-19|May 21-22) July 3 | Aug. 15] Aug. 29 | Sept. 16 
20.35 to | 13.39 to 18.40 | 18.40to “1.58 11.25 1.18 "3.06 
a 19.50 13.06 | 13.06 to 36] 1.14 to | 3.88to | .75 to | 1.18 to 
16.76 8.14 8.14 to 99 | .68 to 4.36 to 1.60 to 72 to 
Quiver Lake........... 16.32 to 4.24 to 51 .51 to 49 3.42 BPs 55 
In almost every case these exceptions to the precise simi- 
larity of movement in production in the two lakes can be cor- 
related directly with some disturbing environmental factor 
potent in one and not equally so in the other, that is, to local 
disturbance in the environmental similarity, as follows: The 
exception on April 24 is due to the earlier appearance of the 
summit of the vernal pulse of production in Dogfish Lake, and 
this in turn is correlated with the greater proportion of shoal 
waters in Dogfish and the greater access of spring water in 
Quiver, both factors favoring the more rapid and complete 
warming up of Dogfish waters. As has been repeatedly 
pointed out, the thermal rise deflects towards itself the vernal 
rise in production. 
Conditions on May 8, when Quiver Lake production doubles 
and that in Dogfish Lake falls slightly, are to be explained by 
the different effect which the hydrographic changes have at the 
two stations. At stages existing at the first of the month 
(7 ft.) there is not sufficient overflow to carry any considera- 
ble current of warm backwaters to the southward down through 
the lake to the river. The content is largely of local impound- 
ing. The slight rise at that time (Pl. XX XI.) would therefore 
tend to increase the local reservoir action, and creek and 
spring waters would most naturally be impounded along the 
usual line of their run-off, in which our Quiver Lake station 
lies (PI. II.), while the plankton-rich backwaters of Dogfish 
Lake are held back, hence the low production in Quiver Lake 
