Igo Burton: The Cleveland Ironstone. 
that the original deposit did not, if at all, extend westward 
much beyond the present escarpment. There must. have 
been during the Middle Lias period much oscillation of land 
and sea levels and alternate encroachments, one on the other. 
As sometimes in mining there is found an entire “ wash-out,” 
and as some of the thinner seams are in places entirely absent,. 
it seems clear that there were many shifting currents sometimes. 
preventing deposits, and at other times removing those which 
had already been laid down. It seems probable that in the 
shallow waters of the period there were mud banks which were 
partly dry land, and that while deposits were being laid down 
elsewhere, there were no accumulations in such areas until 
some further change in level, or a fresh direction of current 
took place. 
The detritus-bearing streams apparently came from the 
north-west, and there is room for the assumption that the black 
shales which so characteristically distinguish the Yorkshire 
Lias are the products of denuded coal measures of the West, and 
that such differences and interruptions in formation, as well 
as changes from shale to limestone as they undoubtedly reveal, 
are due to earth movements having changed the flow of the 
streams in the gathering grounds, the subject of denuding 
action. 
The area over which the ironstone seams extend, and the 
quantity of stone known to exist therein, is not much guide to: 
economic values. But here again one must speak with caution, 
as mines which have been abandoned within the last 50 years. 
because the stone was too poor in quality to be worth working, 
are now being worked profitably. The conditions of iron 
manufacture, the development of improved methods, the 
opening out of new supplies in foreign countries, the freight 
market, state regulation of bounties and tariffs, the contiguity 
of fuel and flux, all have an important bearing upon what Cleve- 
land ore may or may not be possible to use. But the probability 
is that most of the workable stone in Cleveland lies within the 
area 4, J, F, on the map. The northern outcrop of the main 
seam is on the coast east of Saltburn. From there the outcrop 
is by the Western escarpment round to the Kildale Valley ;. 
but the stone lying to the south of the line J, L, F, is poor in 
iron and high in impurities. 
Some of the thin seams are good ironstone, but the cost of 
working renders them of no value at present. 
Two exceptions must be made. At Grosmont, near 
Whitby, the main seam, if at all recognisable, has become 
an attenuated band of about 12 inches thick, but the Pecten 
and Avicula beds each average 3} feet to 2$ feet in thickness ; 
there is a thin shale band in one or both seams, and they are 
separated by a thick bed of shale. Considerable quantities 
Naturalist, 
