Hengshan Fm

Its base marked by purple red moderately thick-bedded sandy siltstone is distinguished from green moderately thick-bedded acidic crystal tuff at the top of the underlying Shouchang Fm.

Its top is exposed incompletely. Next higher unit regionally is the Tongxiang Fm.

The formation is distributed in the Shouchang-Linpu and Chunan-Linan areas of northwest Zhejiang. In the Shouchang-Linpu area, the sediments of the formation vary remarkably in grain size and in thickness. In the Jujia area of Changshan, the formation is made up of purple red sandstone, exceeding 1000 m in thickness. At the locality only 2 km south of Shouchang its lithology has changed to purple red conglomerate, sandy conglomerate and break red fine sandstone, interbedded with each other, occasionally with sediment tuff. In the Duntou basin of Lanxi, it is more than 1042.9 m thick, represented by purple red calcareous siltstone with calcareous fine-medium-grained sandstone, tuffaceous sandstone and rhyolitic tuff, intercalated with tuffaceous gravel-bearing sandstone in the lower part. South of the Meidaban village there exist 14.3 m thick conglomerate, which is equivalent to the upper part of the formation. In the vicinity of Shangmukeng and Yujie at the east end of the Duntou basin there exist 20-100 m vesicular basalt porphyrite intercalated in the base of the formation. In the Chunan-Linan area, the formation is mainly distributed on the northwest side of the Xinanjiang reservoir where the rocks have become coarse in grain size. It is more than 370.4 m in thickness on the Ganwu section of Chunan, and is up to 409.4 m near Jianglingjiao.