102 DESCRIPTION OF THE COAST. 



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, nuculse, am- 

 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. 



6. Hard lias shale, much less fissile than the above, containing nodules and lenti- 

 cular masses of argillaceous limestone, sometimes coated by pyrites. This is 

 occasionally very irony, and, in consequence, much discoloured : twenty to 

 thirty feet. It projects like a solid rock along the breast of the cliff, 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 septiarate, and enclosing dicotyledonous wood, pectines, 

 aviculae, terebratulae, &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 

 lower beds are usually most solid, and project from the cliffs in broad floors, 

 covered with pectines, cardia, dentalia, avicxilse, gryphaese, &c. Thickness 

 variable from forty to one hundred and twenty feet. 



17. Lower lias shale, more solid, less fissile, and generally of coarser and more sandy 

 texture than 15, with a different suite of organic remains, amongst which 

 plicatulas, gryphaeae, and pinnae are, perhaps, most characteristic. Thickness 

 exposed in Huntcliff less than two hundred feet, at the Peak three hundred 

 feet, but the bottom is nowhere seen. 



Huntcliff has the advantage of shewing a greater thickness of thd 

 lower shale than Rockcliff, but its series is very incomplete above ; the 

 upper shale having retired inland beneath the beacon^ There is hardly 

 any diluvial matter observable on the high summits of Rockcliff, but it 

 occupies a large portion of the lower cliffs near Skinningrave ; is in con- 

 siderable quantity on Huntcliff; and gradually thickens toward Saltburn* 



