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The writer discovered the outcrop of the orbicular gabbro with the greatest mass in the world from Mt. Hwangryeong at the downtown area of Busan City, Korea, in 1977. The Busan orbicular gabbro is the first one found in the Asian land, though 13 localities of the orbicular gabbro were already known through the world. The gabbro embracing orbicules intruded the andesitic volcanic rocks of the late Cretaceous Yucheon Group and makes a boss. The association of the igneous reocks in this area may indicate a case of the characteristic igneous activity in the circum-Pacific area at the late Cretaceous Period. The northern peak of Mt. Hwangryeong is inferred to be a volcanic plug, because it is not only composed of fine-breccia bearing andesite, but forms the perpendicular columnar joints. The Cretaceous formation at the southeastern foot of Mt. Hwangryeong is named the Namcheondong Formation in this paper. The formation produces the Cretaceous silicified coniferale stem fossil, but it may not possible for its stratigraphic position to belong to the Sindong Group of the Cretaceous Gyeonasang System. The orbicules in the study area are commonly associated with the schlieren layering, the comb layering and the zonal structure of the calcic plagiocase. Their component minerals are the calcic plagioclase, the mafic minerals as pyroxene, olivine, hornblende and biotite, the iron-bearing minerals, and the secondary minerals as serpentine and chlorite. The SiO2 content of an orbicule sampled for the chemical analysis is 48.5%. The orbicules are generally proto-shelled or single-shelled, and exceptionally multi-shelled, showing the phaneritic texture. An orbicule in orbicule structure is first described in the world. Their core and sshells granular, radial or tangentially oriented texture. The thickness variation of th eshells is not uniform. The greatest orbiculel is in the world is described in this paper, which might be up to about 300cm in long diameter, about 200cm in intermediate diameter, and about 100cm in short diameter of the elongated ellipsoid. The orbicule at present is remained only 1/3 original size due to destructive erosion for a long time. The size of the orbicules ranges from one to 12.5cm in diameter, except the greatest one described above, but is generally less than six centimeters in diameter forming the smaller orbicules. The relatively larger orbicules of slightly more or less than 10cm in diameter occur at some places only. The orbicules of various types are commonly mingled to each other at an outcrop with the moderate size sorting. The orbicules are classified into the category with the core similar to matrix. The origin of the Busan orbicular gabbro is certainly of magmatic, being based on the field evidences explained above. The properties in the parent magma of the orbicular gabbro are thought to have been liquid phase of the low viscosity. The orbicules in the mass are supposed to have been originated by the rhythmic, cyclic or alternative supersaturation and excessive crystallization around nuclei in the gabbroic magma. the orbicules originated from the magma are inferred to be of the equivalents of the concretions in sediments or at the sea floor, the hailstones in the cumulo-nimbus clouds, limestone pearl in cavern, and oolite or pisolite in limestone. The Busan orbicular gabbro emplaced from the basic magma at the end of the Cretaceous Period is located at the southeastern border of the Asian land, as most orbicular rocks do at the other continental borders. Although the present boundary between the Eurasian plate and the Pacific plate runs along the eastern margin of the Japan Islands, it is suggested that the boundary has been located near along the southeastern Margin of the Korean peninsula at the end of the Cretaceous Period. The Busan orbicular gabbro would be authorized to the natural monument of Korea in view of its occurrence, preservation, rarity, greatness and the geological significance.