Continuing his investigations in Mongolia proper, Leder here also discovered earthen kurgans, which, however, differed from those of Siberia by being for the most part surmounted either with circular or rectangular stone structures, or else with monoliths. They are called _Kueruektsur_ by the present inhabitants, who hold them in great awe, and never venture to touch them. Unfortunately strangers also are unable to examine their contents, all disturbance of the ground with spade or shovel being forbidden under pain of death by the Chinese officials, for fear of awakening the evil spirits, now slumbering peacefully below the surface. The Siberian burial mounds have yielded no bronze, a fact which indicates considerable antiquity, although no date can be set for its introduction into these regions. Better evidence of antiquity is found in the climatic changes resulting in recent desiccation, which must have taken place here as elsewhere, for the burials bear witness to the existence of a denser population than could be supported at the present time[580]. Such an antiquity is indeed required to explain the spread of neolithic remains to the Pacific seaboard, and especially to Korea and Japan. In Korea W. Gowland examined a dolmen 30 miles from Seul, which he describes and figures[581], and which is remarkable especially for the disproportionate size of the capstone, a huge undressed megalith 14-1/2 by over 13 feet. He refers to four or five others, all in the northern part of the peninsula, and regards them as "intermediate in form between a cist and a dolmen." But he thinks it probable that they were never covered by mounds, but always stood as monuments above ground, in this respect differing from the Japanese, the majority of which are all buried in tumuli. In some of their features these present a curious resemblance to the Brittany structures, but no stone implements appear to have been found in any of the burial mounds, and the Japanese chambered tombs, according to Hamada, Professor of Archaeology in Kyoto University, are usually attributed to the Iron Age (fifth to seventh centuries A.D.[582]). In many districts Japan contains memorials of a remote past--shell mounds, cave-dwellings, and in Yezo certain pits, which are not occupied by the present Ainu population, but are by them attributed to the _Koro-pok-guru_, "People of the Hollows," who occupied the land before their arrival, and lived in huts built over these pits. Similar remains on an islet near Nemuro on the north-east coast of Yezo are said by the Japanese to have belonged to the _Kobito_, a dwarfish race exterminated by the Ainu, hence apparently identical with the Koro-pok-guru. They are associated by John Milne with some primitive peoples of the Kurile Islands, Sakhalin, and Kamchatka, who, like the Eskimo of the American coast, had extended formerly much farther south than at present.