64 
DESCRIPTION OF THE COAST. 
attains an elevation of two hundred and seventy feet above high-water. 
A sunken portion of the precipices here forms an undercliff, and leaves 
only the upper part of the lias exposed below the conchiferous and plant- 
producing beds before described. But immediately beyond, the scene 
changes, a great dislocation has happened, and the lias beds are uplifted 
on the northern side of it, to such a degree that some conchiferous beds, 
which are usually four hundred feet deep in the lias, appear considerably 
higher than the top of that formation on the south. This will be readily 
understood by referring to the section. 
The uppermost of the beds thus exposed on the north side of this 
great dislocation, belong to a thick series of sandy and irony conchiferous 
strata, which divide the lias clay or shale into two principal parts, hence- 
forward to be termed upper and lower lias shale. The upper one, as being 
peculiarly appropriated to the production of alum, is termed the alum 
shale. These interposed strata are identical in geological characters with 
the marlstone of Lincolnshire, Rutland, and the midland counties. In 
all these counties the marlstone is wonderfully prolific in fossils ; and we 
shall find in the sequel that it is equally productive in the Yorkshire cliffs. 
At the Peak, about forty feet of this series appear, and yield abundance 
of terebratul®, dentalia, aviculm, &c. Below these sandy beds is an im- 
mense escarpment of more than three hundred feet, composed of the 
deeper lias shale, with many layers of ironstone, resting upon more solid 
floors of the same strata. In these solid beds, the lowest probably which 
are exposed on the whole coast, we find the gryphaja incurva, which 
so generally accompanies the inferior beds of lias in the south of 
England. 
Henceforward to the town of Robin Hood’s Bay, the cliffs are com- 
posed of the deeper lias shale, in nearly level layers, surmounted by a 
variable covering of diluvial clay and pebbles. At low-water, the ranges 
of the strata are seen in grand curves sweeping across the whole extent 
of the bay. Beyond Baytown, the cliffs increase in altitude, and a rapid 
declination of the strata towards the north is observed for the space of 
three miles. In consequence of this the deep shale sinks into the sea at 
