Beach Structure in Medina Sandstone. — Fairchild. ii 
The most interesting and significant of these structures are 
the sharp-crested ones. Examples are shown in figures 2, 
5 and 8, plates II, III, IV. Figure 5 shows the one which 
gave to the writer the clue to their origin. The photograph 
does not properly show the clean, sharp, straight crestline. 
Nor does it show what was at first a surprise and puzzle, the 
clear, unmistakable wavelines that swing across the crest in 
varying curves. The overwash of the waves seemed incon- 
sistent with the preservation of the sharp crestline. But this 
made necessary the study of the living beach, with the result 
that precisely similar structures were found upon the beach of 
lake Ontario ; and the process of their construction was stud- 
ied. 
Figures 10-12 and 15, plates V, VI, are from pho- 
tographs of such ridges on the Ontario beach at Sea Breeze, 
near the outlet of Irondequoit lake. Figure 10 was taken late 
one afternoon while the lively waves and currents were build- 
ing the ridge. Figures 11 and 12 show the same ridge the 
next morning when the formative process had ceased. This 
ridge was built on the flank of a larger ridge formed a few 
days previous by a windstorm of greater force. Between the 
two ridges is a decided trough, into which in this case has 
been thrown the wreckage of water plants. The ridge and 
hollovv would on cross-section illustrate those formed millions 
of years ago on the sand beaches of the Aledina sea. This 
trough had a breadth of perhaps ten feet, but others formed 
the same day along the same shore were twenty and thirtv feet 
wide. The breadth of the trough is, however, of little signifi- 
cance as the trough is only a negative or passive eiemcMt and 
depends upon the accident of location of the second ridge with 
reference to the earlier ridge. The width of the same trough 
is also very variable. On the sea shore, with changing level 
of tidal waters, the ridges might sometimes lie far apart. 
In figure 10 we are looking along the crested ridge in the 
direction of its growth as a spit. Before leaving the beach,, 
late in the afternoon, several stakes were set at intervals ex- 
actly in the crestline. At the end of the growing spit a black 
post was set on the center line and at the height estimated as 
the average waterlevel. This post appears in figure 12. The 
following morning another visit was made to tlie place and 
