Geology of Coalhrook Dale, 



437 



The *' blue flat" is a large, misshapen, very fossiliferous ironstone, imbedded in a very dark 

 bluish shale. 



The " chancestone" is an irregular, thickish layer, capping the yard-coal, to which it adhere 

 It is of local occurrence. — See New Hadley. 



The " yellowstone," so called from its external colour, consists of small, very rough, and lumpy 

 nodules, frequently with a conchoidal fracture. 



The " hailstones " generally form two or three layers of large, smooth nodules, imbedded in a 

 light-coloured shale. It is not known by this name south of Ketley. 



The " brickman's measure" consists of two or three layers of ironstone, which break into nearly 

 regular parallelepipeds resembling bricks. 



The " blackstone" IS composed of small and lumpy nodules, with a black, shining coating, and 

 a characteristic conchoidal fracture. They are imbedded in a tough, dark clay, and are not known 

 south of Malinslee. 



The "Ragged Robins" is a very irregular ore, and is occasionally found in the argillaceous 

 sandstone underlying the fungous coal, as at Ketley and New Hadley. 



The nodules of " Chance Penneystone" are small, but smooth and numerous, and are also not 

 known south of New Hadley. 



The above are the beds usually worked in different parts of the coal-field, the higher measures 

 having a very limited range. 



The following tables will show that the number and thickness of the workable measures are 

 much greater in the northern than in the southern part of the field. 



Ironstone Strata. 



North 



South 



Donnington 



Woombridge 8 



New Hadley 6 



Malinslee 5 



Dawley 4 



Lightmoor 3 



Madeley 3 



Broseley 2 



L South of Ditto 1 



Number. 

 7 .. 



Thickness. 



.. 72 



The ironstones thin out in their 

 range southward in descendingorder; 

 thus the Chance Penneystone first 

 disappears, then the Blackstone, and 

 others after; so that at Broseley 

 we find only the Penneystone and 

 Crawstone, and to the south of 

 Broseley the Crawstone by itself. 



Mr. Smith* 

 follows : 



calculates the produce of ironstone per square yard of surface measure to be as 



Thickness i 



■ Stratum. 

 Ft. 



Chance Penneystone 6 



Blackstone 4 



Brick-measure 16 



Ballstone 9 



Yellowstone 9 



Blue flats 6 



White flats 6 



Penneystone 24 



80 



Quantity of Ironstone. 

 Ton. Cwt. Qr. 



3 2 



* Miner's Guide, p. 128 to 132. 

 3 l2 



