LAMPLUGH : EARTH-MOVEMENT IN NORTH-EAST YORKSHIRE. 389 
and when in this position, any plane buried below it must have had an 
opposite or northerly inclination. 
The varying conditions can indeed be roughly exemplified by the 
diagram, if it be pivotted at a point near the southward end of the 
section where most of the planes if prolonged would intersect. Thus 
pivotted, it can be rotated to bring any desired line to horizontality, 
and will then show the relative positions of the others. If one of the 
middle planes, say that of the Grey Limestone or of the Millepore Bed, 
be placed horizontally, the dip of the beds above and below it will be 
in opposite directions, although there is no pronounced break or un- 
conformity in the stratification. The reversal of dip thus revealed 
depends entirely upon the relatively greater thickness of the strata, 
both above and below the plane, at the northern end of the section. 
In the diagram the discordance of dip is, of course, greatly intensified 
by the exaggeration of the vertical scale ; it is really slight, and to be 
reckoned in feet per mile rather than in angular degrees ; in fact the 
cumulative effect of the whole wedge from bottom to top would yield 
a dip of barely 1°. None the less, its consequences as a factor in the 
stratigraphy of the region are important. 
Kendered in terms of feet per mile, the following are the average 
southward dips of the Jurassic planes in the northern 30 miles of the 
section, reckoned from a horizontal Rhsetic base : — 
Corallian — about 63 feet per mile (=1 in 84). 
Cornbrash — about 50 feet per mile ( = 1 in 105). 
Grey Limestone and Millepore — about 43 feet per mile (= 1 in 
123). 
Dogger — about 36 feet per mile (=1 in 146). 
Interpreting the course of events from the relations of these 
planes, we perceive that between the Rhsetic period and that of the 
Dogger the subsidence in the north had been over 1000 feet greater 
than that in the south, and continued in about the same proportion 
throughout the period of the Lower and Middle Oolites, so that by 
Corallian times the northerly subsidence had reached about 2100 
feet more than in the south, with a further increase of uncertain 
amount during the Kimmeridgian period. 
These figures do not, however, give the full measure of the depres- 
sion, as they leave out of account the vertical contraction which must 
have occurred in the column of sediments during their consolidation. 
