98 GEOLOGICAL NOTES ON COAL AND IRON ORE 



characteristic feature in the stratigraphy of this complex 

 is the comparatively frequent alternation between marine 

 and continental sediments. 



On the whole the entire coal formation is constituted of 

 a series of sedimentary cycles within which the succession 

 of rocks seems to be according to following table : 



From Below. 



1. — Quartz Sandstone. 



2. — Black, sometimes pyritic, argillaceous shale with banks of mora 



calcareous clay-material ; the upper levels often show 



prints of plant-roots. 

 3. — Coal-Seam. 



4. — Black argillaceous shale, with plant-roots. 

 5. — Marine, dark and often flinty limestone or calcareous shale. 

 6. — Black, often plant-bearing argillaceous shale. 

 7. — Quartz sandstone, corresponding to No. 1. 



This ideal succession is often found, though not always,, 

 because of interruption of some kind in the course of sedi- 

 mentation. 



The lower age-limit of the coal formation can, according 

 to determination made by -Dr. A. W. Grabau, be put at 

 Youngest Lower Carboniferous; this is the age of a fauna 

 found in marine limestone in the lowermost part of the 

 coal-series. 



The upper age-limit is more difficult to determine 

 because of the absence of marine sediments in the upper 

 part. The youngest marine limestone (see Section) contains, 

 a fauna which according to Dr. Grabau seems to» belong 

 to Upper Moscovian. 



An approximate upper time limit is, however, obtained 

 by the presence of the coal-free, light- coloured, sedimentary 

 formation of which the oldest layers have been found to 

 belong to the Lower Permian (Eothliegende). These form 

 the roof of the coal-series. 



This Permian formation seems to be separated from 

 the coal-series by an unconformity through which at different 

 localities Permian sediments have come to rest upon different 

 horizons of the Carboniferous. At some places a large part 

 of the Upper Carboniferous has been removed, by which also 

 many of the valuable coal-seams have disappeared. 



This is for example the case in the border districts of 

 the Taiyuan basin : in the Western Hills it is mainly 

 bituminous, upper Carboniferous coals that are mined, 

 whereas in the Eastern hills these are absent and the coal 

 is won from the older seams which mainly consist of anth- 

 racite. 



