390 LAMPLUGH : EARTH-MOVEMENT IN NORTH-EAST YORKSHIRE. 
The hard dry shales of the Lias and Oolites in their present state must 
represent a much greater thickness of the original clay- sediment, 
and even the sandstones must have shrunk, though to less degree, 
in parting with the water of sedimentation. The shrinkage began, 
no doubt, almost as soon as the beds were deposited ; it may indeed 
have aided in producing the efiect of slow subsidence in the basin 
when the deeper crust-movement was temporarily in abeyance. But 
the process must be gradual and continuous, and is probably still to 
some slight extent operative. Its measure as between one period 
and another cannot be computed ; but I should think that we might 
safely make an average addition of 10 per cent, to the present measure- 
ments on this account. 
The subsidence reached its maximum in an oval tract truncated 
by the present coast between Scarborough and Whitby. It diminished 
gradually westward and northward, but in these directions the recession 
of the outcrops has greatly reduced the evidence as to the original 
limits of the depressed tract. 
General Deductions. 
The probability that high land bordered the Jurassic basin at 
no great distance on the north and west has long been recognised,* 
and is fully discussed by Fox-Strangways in his General Memoir on the 
Yorkshire Jurassic Eocks.f The westerly thinning of the sediments 
is well displayed in three " Horizontal Sections " of the Geological 
Survey, which run east-and-west, to wit, Xos. 134, 136 and 137, 
particularly in the last ; it is also brought out clearly in some of the 
" Comparative Sections" in the above-mentioned Memoir (Plates III., 
IV. and v.). Near the western escarpment in the Hambleton Hills 
the Lias is shown to be at least 700 feet thinner than in the eastern 
coast-sections, and the Lower Oolites 200-300 feet thinner. In the 
Middle Oolites, so far as they can be compared, there is less difierence ; 
but the sequence in the Hambleton country is incomplete. 
The eastward prolongation of the trough or basin lies beneath the 
North Sea and cannot be followed ; but its longer axis appears tc have 
trended approximately W.S.W. to E.N.E. 
Judging from the position and characters of the Speeton Clay and 
* e.g. A. J. Jukes-Browne, " The Building of the British Isles,'* 
2nd ed. Lond., 1892, pp. 222-237 and pi. viii. 
t Mem. Geol. Surv. supra cit. Chap. XVI., pp. 383-407. 
