NOTES ON THE GEOLOGY OF CLEVELAND. 87 



ft. in. 



Shale 7 0 



Ironstone — good 1 6 



Shale 18 0 



Ironstone — " Avicula-seam" 4 0 



38 6 



In the Grosmont district, however, as I shall have occasion to 

 mention hereafter, the inferiority of these seams to their thickness at 

 Eston is compensated by the presence of other seams above, which are 

 not similarily developed at Eston Nab. The extent of country over 

 which the Cleveland ironstone bands extend cannot be estimated at 

 less than two hnndred square miles, capable of producing from twenty 

 thousand to nearly one hundred thousand tons an acre. The present 

 total yield of Great Britain is something like three and a half millions 

 of tons of iron, from (say) thirteen million tons of stone. Although 

 Cleveland was not worked until 1848, its produce is estimated at 

 six hundred and thirty-three thousand tons of pig-iron from near two 

 million tons of ore. From the extensive mines at Eston alone the 

 vast quantity of two thousand six hundred and twenty tons nineteen 

 hundred weight has been -wrought in one day, — thirteen thousand four 

 hundred and-seventy four tons in a week, — six hundred and thirty- 

 eight thousand six hundred and twenty in one year ; and a total 

 during the past ten years of four millions sixty-one thousand nine 

 hundred and eighteen tons, 



This ironstone is chiefly a carbonate of protoxide, of a greenish 

 grey colour, and yields by government analysis thirty-three per cent, 

 of metallic iron,* although the average should probably be given at 

 about thirty per cent. The following is what is generally requisite to 

 the manufacture of one ton of pig-iron: — ironstone (calcined), two 

 tons twelve hundred weight, or uncalcined, three and a half tons ; 

 coke, one ton fifteen hundred weight ; coal, one ton ; limestone, fif- 

 teen hundred weight. What countless tons of iron, therefore, may 

 be extracted from the vast beds of Cleveland — sufficient to supply, 

 for hundreds of years the whole demand of the British Isles ! 



In every direction from the maximum thickness at Eston, 

 we find the seam grows gradually thinner and thinner, especially 

 towards the south-west, where it may be said to die out at Thirsk. 

 At Swainby also the seam is reduced to about four feet, and 

 divided by rather more than a foot of shale. The seam at Eston is 

 formed of a compact coalition of what are found in other parts as 

 two distinct seams, parted by as much as nearly thirty feet of shale 

 at Grosmont, and the eastern extreme of Cleveland ; the upper of 

 these two seams, as in the Grosmont section, is designated the 

 "Pecten seam," from the vast number of pectines (Pecten cequi- 

 valvis), which are found in it; and the lower the " Avicula seam," 



* See appendix. 



