DAVIS : SECTIONS IN THE LIASSIC AND OOLITIC ROCKS OF YORKSHIRE. 185 
extreme point is a mass of the ferruginous Ironstone Series dropped 
100 feet by the fault. Above this are the Grey Shales, which, being 
soft, have been washed away by the tides, leaving a hollow since 
rilled up with blocks of oolitic sandstone from the cliffs above, and 
always more or less under water. 
Above the Grey Shales the Jet Rock can be seen almost hidden 
by detritus at the foot of the cliff. It is thence thrown by the fault 
to a position on the hills above, immediately below the Peak Alum 
Works, where it has been extensively mined along the face of the 
hill. It has also been much worked at Howedale, further north ; 
from thence it is hidden by Boulder Clay, but reappears at the North 
Cheek of the Bay, forming the summits of Far and High Jetticks. 
Its position in the cliff face is indicated by the terrace, where the jets 
have been dug away, till it reaches the shore with a northerly dip at 
Hawsker Bottom, where its thickness is about 25 to 30 feet. "The 
long white line of breakers that extends at almost all tides from 
Black Nab to Salt wick is caused by the top of this rock ; the lenti- 
cular doggers of calcareous and ferruginous shale being here very hard 
and of enormous size. At very low tides the breakers caused by this 
bed can be clearly seen from the top of the cliffs in the form of a 
curve stretching west till it is due north of the old Abbey."* 
The Jet Rocks are remarkable for their even laminated bedding 
and for the abundance of their fossils. They are of a dark colour and 
interspersed are rows of doggers of blue cement stone with a pyritous 
covering. The doggers contain A. serpentinus and Inoceramus dubius. 
The former is often filled with liquid bitumen, and the doggers them- 
selves smell of mineral oil. At the top of the Jet Rock is a con- 
tinuous band of large doggers, as much as 15 feet in diameter, very 
hard, composed of laminated sandy shale, cemented together by 
carbonate of lime and iron. This continuous dogger band forms the 
roof of all the workings for hard jet, which occurs in greatest quantity 
for about 10 feet below the band. The huge, flattened, lenticular 
doggers may be seen on the shore at Saltwick at low tides, and also 
at South Cheek, between Peak Steel and Blea Wyke, where they are 
* Geology of the Country between Whitby and Scarborough, Memoir Geol. 
Survey, 1822, p. 21. 
