Abstract: In the Jiangsu-Zhejiang-Anhui region, the disconformities at the base of the dolomite of the Huanglong Formation had always been taken as the boundary between the middle and lower Carboniferous in the light of the study of the Nanjing-Zhenjiang Mountain Range by Prof. J. S. Lee et al.（1930, 1935）. But in the past twenty years, some geologists have changed this assignment. Basing themselves only on corals such as Lithostrotion found in the dolomite in Nanjing and Chaoxian county and considering a transition bed between the dolomite and its overlying crystalline limestone as the "basal conglomerate", they separate it from the Huanglong Formation, call it the "Laohudong Dolomite"and assign it to the lower Carboniferous. Some people even consider that this dolomite is different from that in the Jiangsu-Zhejiang-Anhui border region in age and that the latter is stratigra- phically high