364 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [March 12, 



moir on the South Staffordshire Coal-field," will show that bands of 

 Clay-ironstone alternate with the same sediments and in the same 

 way as the coals themselves do. 



5 . Sometimes beds of ironstone rest actually upon beds of coal, as 

 is shown in the following section * : — 



No. 1. 



ft. in. 



Black shale 2 



Chinch 10 



Batt... 5 



Ironstone 2 



Coal 1 2 



Chinch 3 



C lunch and Ironstone 4 



9 9 



" Clunch is a tough clay, breaking into blocks, sometimes rather 

 Sandy, generally grey or yellowish " — a description which applies to 

 many seat earths. 



" Batt f is a highly carbonaceous shale, commonly very compact 

 and splitting into the finest laminse, almost invariably black, and 

 often interstratified in layers with the coal " — an impure coal in 

 fact. Both Batt and Clunch appear from these descriptions to be 

 old terrestrial surfaces. 



6. That calcareous Clay-ironstone has been formed upon a ter- 

 restrial surface is shown by the following section from Millstone- 

 grit shales in Nidderdale, Yorkshire. 



No. 2. 



ft. in. 



Black shale 1 



Nodular limestone 5 



Coal 4 



Seat earth 1 10 



Grit and shale. 



In the South-Staffordshire coal-field, after the splitting up of 

 the thick coal, fifteen bands of Clay-ironstone occur between the 

 top and bottom coals or limiting horizons, thus pointing to a 

 succession of terrestrial surfaces. 



C. i. On the whole, by comparison with the beds of shale and 

 sandstone, the occurrence of bands of Clay-ironstone, and of ferru- 

 ginous limestone, in the carboniferous formations above the base 

 of the Millstone -grit is a very exceptional thing. 



2. The beds of Clay-ironstone are especially characteristic of 

 those great deltas, though from what follows it will appear that 

 there is no reason •prima facie, why they should not be found in 

 other deltoid formations as well. 



We have thus a general view of the varieties, chemical composi- 

 tion, and mode of occurrence of Clay-ironstones. 



* Memoir on South Staffordshire Coal-field, p. 53, 2nd edit. f ibid. p. 16. 



