ROCKCLIFF. 
73 
at Kettleness and near Staithes ; on these lies the great bed of aluminous 
shale, which is so extensively worked, and the whole is surmounted by 
the sandstone cap rock. 
In Boulby cliffs, then, we have the whole series of lias beds exposed, 
and are thus enabled to groupe the minuter parts of the formation into 
convenient natural divisions, and to apply these to complete other less 
perfect sections. 
The following statement, referring by figures and letters to the 
general and enlarged section, presents a summary view of the whole 
lias formation visible in the northern clifls. 
15. Upper lias shale in three divisions : 
a. Alum shale, mostly of a dark colour, and smooth equal texture, fissile into thin 
laminae, very sulphureous, and rich in ammonites, belemnites, nuculae, amu- 
phidesmae, unioniform shells, &c. It is exclusively employed for the manu- 
facture of alum, and varies in thickness from one hundred and forty to one 
hundred and eighty feet. 
b. Hard lias shale, much less fissile than the above, containing nodules and lenti- 
cular masses of argillaceous limestone, sometimes coated by pyrites. r l his is 
occasionally very irony, and, in consequence, much discoloured : twenty to 
thirty feet. It projects like a solid rock along the breast of the cliffs, and is 
excavated into caverns at their base. 
c. Softer layers of alum shale similar to 15 a, with a few courses of ironstone balls, 
and a remarkable line of sulphureous shale in the middle : twenty to forty feet. 
16. Ironstone and marlstone series, consisting of 
a . The ironstone bands, which are numerous layers of firmly-connected nodules of 
ironstone, often septariate, and enclosing coniferous wood, pectines, aviculae, 
terebratulse, &c. : twenty to forty feet. 
b. The marlstone series, consisting of alternations of sandy lias shale, and sand- 
stones, which are frequently calcareous, and generally full of shells. The 
L 
