GEOLOGICAL NOTES ON COAL AND IRON ORE 103 



originated from these pyritic, marine layers. As a matter of 

 fact it is seldom that in one and the same profile we find 

 all the marine horizons that are to be expected. In the place 

 of the missing ones we find more or less considerable layers 

 of the iron-ore "conglomerate" described above. The tran- 

 sition from a fresh, pyritic limestone into an iron-ore layer 

 can often be followed gradually step by step. The trans- 

 formation often begins either in places where the limestone 

 has been more or less subject to cleavage or where it has 

 been broken up by tectonic movements. Here the normal 

 limestone changes to a breccia-like formation of sometimes 

 highly decomposed, rusty, soft limestone and argillaceous 

 limonite. 



The layers of pyritic shale merge into a rust-brown mass 

 of limonite mixed with clay or schistose hydroxide of iron, 

 in which the contours of the pyritized fossils can be traced. 

 It will sometime happen that the primary marine sediments 

 are completely missing in the outcrop and are substituted 

 by a bank of sphero-siderite concretions and rusty clay 

 material. 



Concerning the origin of the ore formations, it seems 

 highly probable that at least part of them originate from the 

 primary contents of pyrite in the sediments and especially 

 in the marine shales. A specially pyritic zone is encountered 

 in the clay sediments in the lower-most part of the Carboni- 

 ferous, where in some localities the contents of pyrite become 

 so enriched that they appear as nodules and are mined for 

 the purpose of sulphur- manufacture (distillation from clay- 

 pots). For the study of the stratigraphical conditions, see 

 Section. 



The iron-ores above described which are found just on 

 top of the marine limestones may have been formed thus. 

 Through oxidation process the sedimentary pyrite has been 

 transformed to sulphate of iron, and part of this has through 

 a still more advanced oxidation, become Hydrate of Iron; 

 another part has by meeting with the calcareous sediments 

 been converted to Carbonate of Iron. 



The Gypsum present in fissures in the Ordovician Lime- 

 stone may have originated from sulphate solutions formed 

 by the above-mentioned chemical reactions within the Car- 

 boniferous. 



The above described observations on the coal and iron- 

 ores in the Carboniferous of Central Shansi indicate that 

 the marine horizons have played an important role at the 



