OKADAIRA SHELL MOUND AT HITACHI.
I．IIJIMA AND Ｃ．ＳＡＳＡＫＩ．
ＧＥＮＥＲＡＬ ＣＨＡＲＡＣＴＯＲＳ ＯＦ ＴＨＥ ＯＫＡＤＡＩＲＡ ＳＨＥＬＬ ＭＯＵＮＤ．
The Okadira shell mound lies on the south western side of a hill called Okadaira，and the eastern and western sides of it are already cultivated for plantations. A white appearance due to broken shells which the ground possesses in the vicinity of this hill is due to the remains of former mounds which have been scattered and destroyed by the farmers.
The length of this mound is estimated about eighteen ken (about 33 m.)in length, and sixteen ken (about 29 m.)in width，and its surface is thickly covered with a number of huge trees. The soil covering the mound is about six inches in thickness. The height of this mound varies from a foot to seven feet. The thickness of the deposit which varies from six inches to three feet,is in its deepest parts about six feet.
The moumd itself is nearly half a ri from the lake of Kasumigaura on the
north-eastern side， and also half a ri distant from a branch of the same lake on the west. And furthermore it is distant about five ri (about 12.5 miles)from the shore of the sea of Kashima(Pacific ocean)of Hitachi.
The evidence that the lake was formerly washed by the ocean is shown by ancient historical records of Hitachi (Hitachi Fudoki)and also from the presence of fossil remains of marine shells at various exposures along the coast.
SPECIAL CHARACTERS OF THE OKADAIRA DEPOSIT.
The Okadaira Mound does not show any remarkable difference in its features from those of the Omori mounds which are described by Prof. Edw.S.Morse in the first memoir of the science department of the University of Tokio in 2539 (1879). As a general rule， objects obtained from such a deposit in both the American and European Continents agree in their general aspect， but each deposit has its special characteristics.