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COASTAL WORKS 239 
out 50 feet high. In the North Atlantic the maxi- 
out 40 feet. Vaughan Cornish (Waves of the Sea, 
J, during a strong gale in December, 1900, measured 
es 20 feet high, and some of 43 feet. The height 
pon the * fetch,” i.e. the width of open water to 
; if the fetch is more than 39 miles the height 
es (H) in feet is one and a half times the square 
e fetch (D), i.e. H = 1:54/D; if the fetch is less 
iles H = 1'5 (2:5 — 4v/D). The heights of waves, 
to the formulas, are as follows :— 
>. 
5, 
Vave Height. 
Fetch, Wave Height. 
Fetch. ‘Wave Height. | 
5 
3 ft. 
5 ft. 6 in. | 
7 ft. 1 in. 
30 miles = 8 ft. 4 in. 
40 ,, =gft. 5 in. 
50 ,, =10ft. 6 in. 
100 miles = 15 ft. 
200 ,, =2Ift.5in, 
300 ,, = 26ft. 
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res in Lake Geneva are 8 feet high where they have 
40 miles, those on Lake Superior 20-25 feet high 
ch of over 300 miles. 
ith of disturbance of a wave is equal to its length ; 
num length of ordinary waves in the Atlantic is 
nd they disturb fine sediment to the depth of about 
or 100 fathoms. The action diminishes rapidly 
a. The displacement of water particles at a depth 
he length of the wave is only xls and at double 
Lis only yggsyy of that of the surface. At special 
ves and currents move material far below the 
imit of wave action. Lobster pots in the English 
re sometimes filled with coarse shingle at the depth 
i feet. Seaweeds which live not less than 200 feet 
vashed ashore with stones attached to their roots, 
have been torn from the sea-floor by waves. The 
!legraph cables is cut by drifting sand at the depth 
;, and silt is moved at greater depths. 
nsport of beach material depends on the angle at 
‘es strike the shore. A wave which rushes obliquely 
ach returns by the shorter steeper course at right 
the shore ; it carries material along a zigzag course. 
rash may be concentrated and strike a more power- 
han the oncoming wave; thus at Dunbar a wave 
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