This study was conducted to reclassify Dongsong series based on the second edition of Soil Taxonomy and to discuss the formation of Dongsong series distributed on the lava plain atCheolweon inKorea.Morphological
properties of typifying pedon of Dongsong series were investigated and physico-chemical properties were analyzed according to Soil Survey LaboratoryMethodsManual. The typifying pedon of Dongsong series has
brown (7.5YR 4/2) silty clay loam Ap horizon (0-16 cm), brown (7.5YR 4/2) silty clay loam BA horizon (16-22 cm), brown (7.5YR 4/2) silty clay Bt1 horizon (22-50 cm), reddish brown (5YR 5/4) silty clay Bt2 horizon (50-92 cm), and brown (7.5YR 4/3) silty clay loamBt3 horizon (92-120 cm). It occurs on lava plain derived frombaslt materials. The typifying pedon has higher bulk density than 0.90 Mg m-3. That can not be classified as Andisol. But it has an argillic horizon from a depth of 22 to more than 120 cm and a base
saturation (sumof cations) of less than35%at 125 cmbelow the upperboundary of the argillic horizon. It can be classified as Ultisol, not as Andisol orAlfisol. It has aquic conditions forsome time in normal years in one
ormore horizons within 50 cm of the mineral soil surface, redoximorphic features between a depth of 25 cm and a depth of 40 cm from the mineral soil surface, and redox concentrations and 50%or more redox depletions with chroma of 2 orless in the matrix within the upper12.5 cmof the argillic horizon. Therefore it can be classified as Aquult. It has episaturation, and keys out as Epiaquult. It has 50%ormore chroma of 3 or more in one ormore horizons between a depth of 25 cm fromthe mineral soil surface and a depth of 75 cm. It
can be classified as Aeric Aquult. Dongsong series have 35%ormore clay at the particle-size control section,
and have mesic soil temperature regime. Therefore they can be classified as fine, mesic family of Aeric
Epiaquults, not as fine, mesic family of Typic E iaqualfs. The Quarternary volcanic activities occurred in Jeju Island, Ulrung Island, Baekryeong Island, Cheolweon area, andMt. Paekdu et al. in the Korean Penninsula.
Most of them belong to the central eruption type, but Cheolweon area may be of the fissure eruption type.
Dongsong series occur on Cheolweon lava plains derived from basaltic materials. Most soils distributed in Jeju Island and derived frommainly pyroclastics are developed as Andisols. But Dongsong series distributed
in Cheolweon lava plains which have a relatively dry climate and derived from basaltic materials are developed as Ultisols.