GEOLOGY AND ORE DEPOSITS OF SU-AN Ö 



A. Topographic Features 



The mining region (see PJ. IV.) lies in a Inll}^ interior, rising 

 barely oOO m above sea-level, at the northern foot of the granitic 

 On-jin-san ^\ 1117 m high, which forms a prominent land-mark of 

 the district. The granitic stock, now being dismantled in the 

 general process of denudation, stands out above the surrounding 

 country, and its eruptive mass has an intimate relation to the 

 economic resources of the region as the " ore-briuger " of the 

 metalliferous deposits. 



The country around the eruptive stock is much disturbed. 

 Tilted and uplifted edges of blocks of the earth's crust form the 

 series of lengthwise and crosswise ridges which characterizes this 

 part of the peninsula '^\ The general strike of the rocks is N. 60° W. 

 with variable dips to the N. E., and the strata are all tilted up 

 to the S. and faulted down on the same side. The series of these 

 tectonic lines finds its expression in the equatorial ridges. These 

 are old lines of dislocation, and were crossed later by another 

 series of dislocations which lifted up the western and sometimes 

 the eastern margin throwing down the blocks on either side. The 

 younger ridges so produced are here designated the meridional 

 ridges and trend N. 20° W. The network of the above-mentioned 

 tilted edges of crustal blocks determines the fundamental elements 

 of the topography and the drainage of the area. 



The Sijig-gyöi-gang ^"\ a large tributary to the Tai-dong ^^ river, 

 follows a course parallel to the equatorial ridge. At about the 

 middle of its course, there is located on its northern bank the large 



1) ;SÄllJ 



2) This Journal, Vol. XtX. Article 1, Geotectonic Map. 



3) mwa. ^) ±UK 



