100 GEOLOGICAL NOTES ON COAL AND IRON ORE 



and the relation of coal seams to the marine horizons. 

 These seams may here be considered to have been swamps 

 situated within a low-lying shore district or lagoons in which 

 large quantities of rotten plant-remains have accumulated and 

 afterwards through an invasion of the sea been saved from 

 annihilation. These transgressions of the sea are now 

 marked by the presence of the marine limestones. 



The frequent occurence of marine sediments as inter- 

 calations in the continental deposits and the variation of 

 petrographic character of sediments in a direction perpendi- 

 cular to the stratification, shows that the region in question 

 has been subjected to rhytmic subsidences with accompany- 

 ing minor transgressions of the sea. Parts of these invaded 

 areas may possibly, in the course of continued sedimentation, 

 have been separated from the sea, and the continental 

 sediments have accumulated until, through a renewed sub- 

 sidence and renewed transgression, the same cycle has been 

 repeated. 



Amongst the Carboniferous coals we find, as mentioned 

 above, in the border-districts of the Taiyuan basin, both 

 anthracitic and bituminous seams. The latter are best deve- 

 loped in the Upper Carboniferous and may represent the 

 time for maximum coal-formation. The Lower Carboni- 

 ferous seams contain either semi-anthracitic or bituminous 

 coals; the former predominating. 



The largest coal mines in the Western margin of the 

 Taiyuan basin are : Fu Ho Yao, Tung T'a Yao, and Lo T'o 

 Pq Yao which work in the Upper Carboniferous bituminous 

 zone. The seam has in outcrop the thickness of \ to 2 

 metres, but the mining is generally going on where the 

 coal, through formation of pockets, attains a thickness of 

 3 — 4 metres. 



The largest semi-anthracite seams occur in the sub- 

 stratum of the thick, Lower Carboniferous, marine lime- 

 stones. 



One of the largest anthracite mines in the West is Hsi 

 Sheng Yao. 



In the North Eastern marginal hills at the Taiyuan 

 plain, the largest part of the Upper Carboniferous became 

 eroded away at an early stage — as mentioned above — and the 

 maximum bituminous seams are therefore absent. A not 

 inconsiderable part of the coal mined here is Lower Carboni- 

 ferous, Semi- Anthracite and Lower Carboniferous, Bitu- 

 minous coal. The outcrops of the anthracite seams seldom 

 exceed 1 metre in thickness. 



