The Jiangshan-Shaoxing Fault is generally regarded as the boundary between the Yangtze Block and Cathaysian Block in the Lower Yangtze Area. However, It was a suture formed in Proterozoic. The relationship between the Yangtze and Cathaysian Blocks during the Caledonian Period is still a problem. The Proterozoic metamorphic rocks form the core part of an anticlinorium in northeastern Jiangxi and southern Anhui. The Cambrian and Ordovician sediments on its two limbs vary from basin-slope facies to platform facies from insides toward outsides. The facies boundaries mark the Yangtze Platform margin along a line from Shitai to Jingxian in southern Anhui, and the Cathaysian Platform margin along a line from Jiangshan through Kaihua to Lin’an in western Zhejiang during Cambrian and Ordovician. The intermediate area occupied by metamorphic rocks was a part of the “Jiangnan Basin” at that time. An important change on the sedimentary pattern happened at the end of Ordovician. This area transferred into a tapered “Jiangnan Uplift” - a terrigenous material source area. The deformation of the Cambrian and Ordovician sedimentary rocks in two limbs of the anticlinorium becomes stronger from outsides toward insides where the isoclinal and overturned folds appear. This indicates that the Jiangnan Uplift belongs to a Caledonian fold belt. The Silurian terrigenous sediments with large thickness occur on both sides of the Jiangnan Uplift and its northeast. The sedimentary sequences vary from shallow marine sediments upwards into littoral or deltaic sediments and finally into non-marine sediments. The marine sediments become increasingly abundant towards northeast and developed in later Silurian in Jiangsu Province. Here the Silurian rocks are overlain disconformably by the Devonian strata. They were probably deformed until the Indosinian period. The Caledonian foldbelt and Indosinian foldbelt coexist between the Yangtze and Cathaysian Blocks in Lower Yangtze Area.