88 
THE GEOLOGIST. 
owing to the abundant remains of Avicula cygnvpes in it. Towards 
the east the "Pecten seam'-' acquires more the concretionary spheroidal 
form, as usual %vith argillaceous deposits, and approaches nearer in 
appearance to the hard, compact clay-stones of the coal-measures at 
Bierley and Low Moor, As the diminution in thickness towards the 
south-east and west from Eston is veiy gradual, it is impossible to 
fix any line of demarcation to point out the exact boundary within 
which it is of su^c.ieni; value to be worked.. , . _ ^ 
An interesting paper was read by Mr. H. C. Sorby, F.Gr.S., iDefore 
the West Riding 'Geological and Polytechnic Society,* in which the 
writer endeavom^ed to show that the Cleveland ironstone was altogether 
an altered limestone-rock, in which the carbonate of lime had been 
changed to carbonate of iron, by the percolation, probably, of some 
chalybeate water, and that the ironstone was not deposited in its present 
condition. I confess that I am not inclined to adopt those views 
without farther examination, as I think the whole analysis of the ore 
does anything but favour such a theory. In concluding my no1:ice of 
this most important division, I need only add that these Lias bands are 
very extensively wrought, at Eston, Upleatham, Codhill, Hutton" 
Lowcross, Belmont Banks, Rosedalef on the coast, Grosmont in 
Eskdale, and several other parts of Cleveland. The usual royalty- 
rent paid in the district varies from fourpence halfpenny to eight- 
pence per ton of twenty-two and a half hundred weight ; and, so 
cheaply may it be worked, that it can be sold with profit at half-a- 
crown a ton at the mine's mouth. Such brief statistics may be of 
interest to those readers who are in any way connected with this 
great branch of manufacture. I now ascend to 
d, The lj])]jer Lias Shales, which also possess great importance in 
an economic point of view. After about thirty to forty feet of har(T 
sandy shale, which is the lowest rock in the upper Lias, we find what 
is generally called the " Hai'd Jet Rock," a variable shale twenty feet 
in thickness, enclosing irregularly jet and pyrites. On the coast, as 
at Kettleness, the rock is harder and more productive of jet than in 
the interior of the country : the raw material is, according to quality, 
worth from two shillings to twelve shillings per pound, and the total 
value of the jet-manufacture at Whitby, whither it all goes from this 
district, is estimated at twenty thousand pounds per annum. Owing 
to the great quantity of iron-pyrites, or nodules of sulphuret of iron, 
which these shales contain, it not unfrequently happens that upon 
being dug out in the search for jet, and exposed to the action of 
moisture and the atmosphere, the sulphur combines with the oxygen 
of the air and of the water, and in this decomposition sufficient heat 
is generated to cause spontaneous ignition. An instance of this 
decomposition occurred not long ago in Westerdale, and caused no 
little wonder amongst the homely inhabitants; it is, however, of 
* Report of Society's Proceedings, 1856-7, p. 457. 
t There are two " Rosedales" in this district celebrated for their ironstones : 
one near Staith on the coast, and the other fifteen miles inland. 
