NOTES ON THE GEOLOGY OF CLEVELAND. 
89 
frequent occurrence on the coast at Runsmck Bay. Here, it is 
scarcely necessary to remind the reader, is a most marvellous pro- 
fusion of Ammonites, Belemnites, &c., and an abundance of the now 
familiar remains of Ichthyosauri and Plesiosauri. An excellent 
section of these rocks, and a delightful field for geological observa- 
tion, will be found in the quiet and picturesque bay of RunsAvick. 
Above this jet-rock are about eighty feet of shale with ferruginous 
nodules, irregularly interspersed, and for the most part aggregated 
round Ammonites and other organic bodies. Being very compact 
and argillaceous, they closely resemble some of the clay-ironstones of 
Derbyshire, and claim a similar, though far from a synchronous 
origin. Above this shale, again, we reach the fine argillaceous 
deposit so well known by the name of " alum- shale," which is from 
eighty to one hundred feet in thickness, and has been worked for the 
manufacture of alum since about the year 1594, when alum-works 
were first introduced into the district of Guisborough, by Sir Thomas 
Chaloner, where these shales have ever since been more or less ex- 
tensively wrought. Scattered up and dowTi through the whole 
length of Cleveland, we find traces, in vast heaps of calcined shale 
and large excavations, of abandoned alum- works, as at Carlton Bank, 
Kirby Bank, above Great Ayton and several other places, whilst we 
find in present operation the works near Guisborough, at Boulby, 
and at Kettleness. The process of manufacture is simpl}^ as follows : 
the decomposition of the shale is accelerated by being burnt in largo 
heaps by the manufacturer, who avails himself of the carbonaceous 
character of the shale, and the sulphm^ of the iron is changed into 
sulphuric acid, which forms a sulphate of iron and alumina ; by sub- 
sequent processes of evaporation, the sulphate of alumina is purified, 
and potash is added to render the salt crystallizable. 
Above the alum-shale is a stratum about twenty feet in thickness, 
which is usually termed the " Cement-rock," from its containing 
numerous calcareous nodules, which are used in the manufacture of 
Roman cement. These nodules will, for the most part, be found to be 
an aggregation round an organic nucleus ; and by baking them until 
they divide, I have frequently procured most beautiful specimens of 
fossil Ammonites. Above this is found, in a perfect section, a deposit 
of about four feet of indurated clay known as the "soft jet-rock," from 
its containing a quantity of jet, inferior however to that in the hard 
jet-rock, of which I spoke before. This rock, in opposition though 
it be to many, I shall make the highest one and the conclusion of the 
Lias formation, the upper division of which, as I have described it 
above, may in summary be given as follows : 
ft. in. 
Soft jet rock about 4 0 
Cement-rock „ 20 0 ft. in. 
Alum-shale (used in manufacture of alum) 80 0 to 100 0 
Alum-shale (not so used, and with many 
nodules) 60 0 to 80 0 
Hard jet rock 18 0 
Hai-d sandy shale 20 0 to 40 0 
VOL. IV, M 
