316 WAVES OF SAND AND SNOW 



extending from one set of spring tides to the next 

 with the time of neap tides between. At this time 

 of year, however, the spring tides are of smaller 

 range than near the Equinoxes. The tables 

 (pp. 322-5) show the results of the measurements, 

 and should be consulted before the reader proceeds 

 with the text. 



On comparing the table on p. 189 with the first 

 it will be seen that the slight diminution in average 

 length between June ist and 4th was due to the fact 

 that the front ridges moved more slowly than those 

 at the back. The ridges were not contour lines, as 

 the ridges of swell -formed ripple -mark usually are, 

 but lay along a slope inclining downwards to a low- 

 water channel on the north-west, so that the last 

 runnings of the water from the plot were along the 

 troughs of the waves — i.e., in a direction at right 

 angles to the current which produced the waves. 

 As the tides diminished after springs, the length 

 of the waves diminished very slowly, but their 

 height fell off rapidly, and at the time of neap, 

 tides they were nearly obliterated, the surface of 

 the sandbank being almost smooth., The average 

 level of the sandbank was, however, unchanged. 

 When the tides increased after neaps, well-defined, 

 steep sand-waves were again formed, which grew 

 in height and length. 



