LAMPLUGH : EARTH-MOVEMENT IN NORTH-EAST YORKSHIRE. 385 
Starting at the bottom, we have in the Rhaetic beds a typical 
example of horizontal sedimentation. From their faunal and litho- 
logical characters, we recognize that these beds were deposited in a 
shallow sea which invaded a broad inland basin already levelled up 
with the sediments of a salt-lake constituting the Keuper Marl. 
Though sparingly exposed, these Rhaetic beds are believed to extend 
unbrokenly beneath the Lia s from the Tees to the Humber. Therefore 
they afford a most convenient basal plane from which to reckon 
Jurassic earth-movement. 
The Gryphaea-beds of the Lower Lias and the Pecten-beds of the 
Middle Lias carry evidence of original uniformity of depth over a wide 
area, and afford information as to the progress of the movement 
during Liassic times. 
The Dogger at the base of the North Yorkshire Oolites usually 
marks a break in the sedimentary sequence ; but in the coast-sections 
at Blea Wyke the transition from Lias to Oolites is gradual, through 
passage-beds which indicate progressive shallowing of the Liassic 
sea. The irregularities produced at the close of the Liassic period 
by tilting and perhaps locally by faulting appear to have been level- 
led up by the Dogger ; so that, although its base is uneven, its top 
may be accepted with fair confidence as originally a horizontal plane, 
on which the lowest beds of the Estuarine Oolites were accumulated. 
The relation of this plane to that of the Rhaetic affords us a useful 
measure of the net displacement during Liassic times. 
The relatively thin Marine Bands intercalated with the masses of 
estuarine or fresh -water sediments which form the major portion 
of the Lower Oolites of North Yorkshire have long been recognised as 
having been deposited in shallow water during wide-spread incursions 
of the sea on a subsiding tract. They are three in number — the 
EUerbeck Bed, with its southern equivalent, the Hydraulic Limestone ; 
the Millepore Bed ; and the Scarborough or Grey Limestone ; and 
though their value is somewhat impaired by the fact that they are 
not continuous over the entire area, they furnish us with three trust- 
worthy and complementary datum-planes fulfilling all the required 
conditions. For generalizing purposes, it will be most convenient to 
take the Grey Limestone in the northern part of the area and the 
Millepore Bed in the southern part as representative of the three, 
since all three yield practically the same evidence. Some points of 
minor consequence, with which I do not propose to deal, may, however, 
