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PACIFIC SCIENCE, Vol. XVII, April 1963 
FIG. 1. Map of Kyushu, showing the position of 
Tsuyazaki. 
DESCRIPTION OF AREA SURVEYED 
The peninsula of Tsuyazaki (Fig. 1) lies at 
130° 29' E, 33° 47' N, about 20 km north- 
northeast of Fukuoka City, and faces on the 
Genkai-nada. The peninsula protrudes from 
general coast line of sandy beach, and consists 
of hills more than 100 m high. Although these 
hills are for the most part composed of palae- 
ozoic sedimentary rock, there is a granite zone 
on the west side facing the sea, and a basalt 
layer lying above the 100 m contour line. Along 
the middle of the shore of the peninsula, there 
is a sandy beach called "koi-no-ura.” The rocky 
area, where the Sargassum community develops, 
occupies the northern and southern parts of the 
peninsula. An outline of the geological structure 
of the area concerned is shown in Figure 2. 
Although the nature of the bottom is rocky 
where the shore is exposed to strong wave ac- 
tion from the intertidal zone to a depth of about 
10 m, or of boulders in more sheltered places, 
such hard bottoms give way to sand at the rela- 
tively shallow depth of 15 m or less. Sandy 
bottoms are met in deeper places all around the 
peninsula. 
On the coast of North Kyushu, tides are semi- 
diurnal, and the diurnal inequality of the tides 
is not remarkable. The spring tidal range is 
about 1.9 m, and 1.4 m at neap tide. According 
to the "Coast of Kyushu Pilot” (1947), in the 
Kuraraseto passage, lying to the north-northeast 
about 10 km from Tsuyazaki, the tidal current 
flows towards the north from 4 hr after low 
tide to 4 hr after high tide, and towards the 
south from 4 hr after high tide to 4 hr after low 
tide. The tidal current flowing north reaches a 
speed of 2.8 knots. Near the shore of the area 
surveyed, the tidal current runs even faster 
around Tsuzumi islet, lying to the north of the 
peninsula, and may reach a maximum speed of 
more than 1 knot. The current moves more 
slowly near Sone-no-hana and Kyodomari. 
Stronger waves and swells are generated with 
north or west winds, influenced by the topogra- 
phy of the neighbouring area. Hence, the north 
and west sides of the peninsula are more ex- 
FlG. 2. Geological map of the peninsula of Tsuya- 
zaki (after Takehara, 1937). 
