In this paper I shall present a theory a little different from those which have been done on origins of spits, bars, coastal dunes and some other similar geographical features, such as off-shore bars, land-tied islands and so on, by referring to the results of my survey on the Tagonoura Dune.
I. Tagonoura Dune.
The Tagonoura Dune lying between the mouth of the Fuji River and the Ushibuse Hill on the north coast of Suruga Bay, central Japan, is composed of the following sub-divisions:
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Major characteristics of the Tagonoura Dune are as follows:
1) The dune lies east-west curving gently northwanrd, and is 22 kilometers long, 200_??_900 meters wide and 5_??_10 meters high (20 meters at the highest).
2) The dune has an anticline-like structure dipping 5°_??_10°S•5°N with an east-west strike.
3) The dune is formed both of the upper group chiefly composed of upper aeolian deposits and of the lower group chiefly of bar deposits. The lower group further consists both of upper part of the upper bar deposits and of the lower bar deposits covered with lower aeolian deposits.
4) The formation composing the bar deposits shows apparently a bedding 10 centimeters thick.
5) The sand and gravels in the formation of the sand bar are well sorted.
6) The bar deposits contain more or less silt in it.
7) In the bar formation are several sheets of fine siltose gravel bed sandwiched.
8) In the bar deposits is found a thin scoria bed.
9) Several sheets of lens-like gravel bed are found. Gravels are larger than 4 mm. in diameter.
10) In the bar deposits a cross-bedding is perceivable.
11) In the lower group are found five disconformities and one unconformity.
12) Relation between upper and lower groups is of unconformity.
13) In the lower group can be percieved a face eroded by the current inside the sand dune.
14) The chief supplier of the materials composing the Ukishima Dune is the Fuji River and that of the Sembon Dune is the Kano River.
15) In some cases the bar deposits are composed of great boulders bigger than 2 meters in diameter, e. g., at Ôse Point on the northwest coast of the Izu Peninsula.
II. On the origin of some geographical features similar to coastal dune.
1) Greater part of the materials composing the dune is supplied from mountains in the watershed of a nearby river or from the coast eroded by waves.
2) One of the two chief forming agencies of the dune is stream, and the other shore current.
3) The materials carried ashore by a long shore current are deposited long and narrow on the bottom of shallow sea, growing later with regression into a bar, the beginning stage of a coastal dune.
4) With surfs and sea breezes aeolian deposits settle on a bar and the coastal dune is formed.
5) Regression which did much for the formation of the coastal dune is supposed to have occurred in the Cenozoic glacial age.
6) The Tagonoura Dune is presumed to have been formed before 100 B. C. from archaeological and paleontological researches.
7) Developmental differences on the bed of shallow sea cause such different topographies on the ground as spits, bars, off-shore bars, land-tied islands, etc.
I believe that the above-mentioned interpretations are applicable to the study of origin of most geographical features similar to a coastal dune which are found in Japan in a large number.
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