256 
flat top of the delta dug out the groove for a few feet, but was deflected 
upward and spread out into a thin sheet before reaching the edge. This 
interpretation was confirmed by the records of rainfall and lake level kept 
by the Rochester water works at the foot of the lake, which is the source 
of public supply for that city. These records are as follows: 
Date. Hours. Rainfall. Lake Level Above Datum. 
July. 5 12:30-7:00 p. m. 921 in. 1.736 ft. 
eG In the night. 2.349 “ 2.926 “ 
ae 10:00-11:00 p. m. 546“ 3.106 “ 
5858 ps ahh) ess Soe Meee ee OR Sah er 3.126 “ 
“ 18 8:00-11:00 a. m 101 “ 2.176“ 
“19 In the night. 12397" S 2.296 ** 
Siete Se 2:00-6:00 p. m. 160%) eccs aatos 
tae) In the night. .864 “ 2.546 
oe 7) 1 ia Se etinae seen ate _ 11 iew a RRO Serre 3.186 “ 
| 
These deltas were begun during the heavy rains of July 5-7, when 
3.516 inches of rain fell and the lake rose 1.39 feet, most of the work being 
done in the night of July 6, when 2.35 inches of rain fell. They were com- 
pleted July 18-20, when 2.97 inches of rain fell and the lake rose 1.01 feet. 
These miniature torrential deltas furnish suggestions for the interpreta- 
tion of similar but larger features which mark the shore lines of the tem- 
porary glacial lakes formerly occupying the Finger lake valleys. 
A similar flat-topped, steep-sided feature caught the writer’s eye on 
the east side of Honeoye Lake. Projecting from the steep hillside like a 
bracket it rose 200 feet above the lake, suggesting by its bold and sym- 
metrical outlines an artificial origin similar to that of the dump pile of a 
mine (Fig. 2). It proved to be a torrential delta built at the mouth 
of Briggs gull. Its finely curved front slope, about 150 high, is as steep 
as the material will lie. Its flat top is traversed by a channel twenty feet 
wide and three feet deep which extends to the edge and is continued by a 
similar groove in the steep face. The southern side cut away by the main 
stream shows characteristic foreset beds of sand containing large frag- 
ments of shale near the top. Briggs gull now drains a basin of about six 
square miles. A heavy rain with rapid melting of ice or a sudden diversion 
of drainage by the breaking of an ice dam in glacial times may have en- 
abled the stream to build this delta in a few days or weeks. Briggs delta 
helps to account for the anomalous distribution of glacial lake deltas. 
Similar features are numerous in the Finger lake valleys. Not their 
presence but their absence from the former mouths of many streams seems 
