432 IRON IN THE LIAS. 



Oxides of iron more or less siliceous are found in the Cambrian rocks 

 of Counties Longford and Cavan, but chiefly in the district between 

 Granard and Carrick-on-Shannon. 



Scotch Iron Ores. In Scotland most of the iron ores occur in the 

 coal measures of Ayrshire, Lanark, and the country between the Firths 

 of Forth and Clyde. The seams of ironstone vary in thickness from 

 a few inches to two feet, and are mostly blackband clay ironstone, 

 which yields 30 to 40 per cent, of metal, and is similar to the ores of 

 North Staffordshire. Iron oxide ores are worked in small quantity 

 in Shetland, Aberdeen, at Auchencairn in Kirkcudbrightshire, at 

 Garleton in Haddingtonshire, and Whytock and Muirkirk in Ayr- 

 shire. The hematite at Auchencairn is similar to the kidney ore of 

 Whitehaven. 



Permian Iron. 



In the Permian beds iron ore occurs in hollows or basins, as at 

 Mwyndy, near Llantrissant. Sir Henry De la Beche recorded the 

 occurrence of hematite un conformably covering the coal measures near 

 Llanharran, in Glamorganshire. 



Liassic Iron Ores. 



Cleveland Ironstone. The Cleveland ironstone is well seen in 

 the Yorkshire coast between Old Peak, south of Whitby, and Middles- 

 borough-on-Tees. It extends in a basin with several minor undula- 

 tions, descending below the sea-level north of Robin Hood's Bay, and 

 reappearing at Kettleness, and between that place and Staithes 

 another synclinal fold sinks the ironstone below the sea-level. The 

 best section is to be seen at Boulby. The iron ore continues to rise 

 in the cliff, till at Huntcliffe it retires from the coast. It is then 

 followed inland by way of Arncliffe, extending through the whole of the 

 Cleveland Hills, and turning south-east, it disappears under the oolites. 

 Usually the several seams of ironstone are parted by shale. They are 

 frequently oolitic, and contain Pecten cequivalvis, Avicula cynipes, 

 and other Lias fossils. 1 They thicken towards the north and ulti- 

 mately unite, so that in the Eston Hills the ironstone has an aggre- 

 gate thickness of 18 feet. The thick beds, however, are not always 

 the most valuable, for though the ore at Grosmont has a thickness 

 of nearly 14 feet, only 6 feet 6 inches of it are worth extracting, the 

 remainder being interstratified with seams of shale. The ore yields 

 30 per cent, of iron, and has much the aspect of a sandstone. Mr. 

 Bewick believes that the ironstone covers an area of 420 square miles. 

 He estimates the average yield of every acre at 20,000 tons, and the 

 total supply of the district at 4,820,659,200 tons, an amount which 

 would supply 200 blast furnaces for 680 years, and enable each to turn 

 out 200 tons of pig iron in a week. 2 



1 Mem. Geol. Surv., " Iron Ores of Great Britain," Part i., W. W. Smythe, 1856. 



2 Jos. Bewick, " Geol. Treatise on the District of Cleveland," 1861. 



