GEOLOGY OF KOREA 75 



Daido System:— Tliis is not a continuous group of rocks, and 

 divisible into five formations, distant from one another or in uncon- 

 formity. The oldest one, the Lower Daido Formation, consists of 

 basal conglomerate and alternations of shale and sandstone intercalating 

 anthracite seams. The flora of this Foi-mation consists of a mixture 

 of Rhaetic and Oolitic plants. Animal remains ai'e scarce and an 

 jimmonites found in the Formation was identified with one of the 

 Liassic forms of the Japanese Islands. The next division, the Middle 

 Daido Formation, also consists of alternations of shale and sandstone, 

 intercalating thin anthracite seams. The plants obtained seem to be 

 a little younger than those of the Lower Daido and is tentatively 

 regarded as Middle Jurassic. The third formation is the Lower 

 Keisho Formation which again consists of alternating layers of shale 

 and sandstone, intercalating thin anthracite seams near its base. 

 It is considered to be Upper Jurassic from the plants iound in it. 

 The fourth or the Upper Keisho Formation, in N. and S. Keisho-Do 

 is characterized by its rocks— flinty shale, red shale, tuff, and repeated 

 flows of porphyrite, and covers the Lower Keisho Formation with its 

 thick basal conglomerate, the relation between being apparently con- 

 formable. But the presence of a slight unconformity is also reported 

 by some authors. The Formation yields the Lower Cretaceous plants. 

 The Upper Daido Formation in Kokai-Do and Heian-Do petrologically 

 and palaeontologically resembles this Formation. The fifth or the 

 uppermost division, the Fukkokuji Formation, is mostly made up of 

 quartz-porphyry and felsophyre in flow^s, and a small proportion of 

 their agglomerate a.nd tuft' at the base. These rocks are intruded by 

 a granite which is considered to be comagmatic with the acidic vol- 

 canic lavas. This Formation is covered by the Older Tertiary, and as 

 the surface on Avhich the latter lies is deeply eroded, the former is 

 considered to be Cretaceous in age. 



Tertiary:— The Tertiary System is found in extremely limited 

 areas, that is, in small areas mostly along the eastern coast. It is 

 divisible palaeontologically and stratigraphically into the Palaeogene 

 and Neogene, the latter being known only in the Choki distric', N. 

 Keisho-Do and on the southern coast of the island Saishu-to in the 

 strait of Tsushima. 



The older Tertiary is terrigenous or marine in origin, consisting 

 of sandstone, conglomerate, shale and flows of volcanics, intercalating 



