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 hundred 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 gi^eenish 
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 ; hmestone, 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 (Peden cequi- 
valvis), which are found in it; and the lower the " Avicula seam," 
* See appendix. 
