THE STEUCTURE OF THE GULLY, DURDHAM DOWNS. 71 
been that in Liassic times the little group of shales in the 
notch must have been constantly saturated with water. 
Even the upper parts of the limestone band or bands would 
be much altered by this ; and the shales would be reduced to 
a semi-fluid unstratified paste except in their deeper parts. 
Then an unknown thickness of Mesozoic deposits was laid down 
on top of them. The consequence was inevitable — re-strati- 
fication of the paste. Two factors combined to bring this 
about. Eirstly, when saturated with water, mud tends to 
become horizontally stratified by re-arrangement of its con- 
stituent particles, and the possibility of re-stratification is 
ulluded to by Sorby in Q.J.G.S.j vol. xxxvi., p. 67, when 
-pointing out this tendency. 
Secondly, the weight of the superincumbent Mesozoic rocks 
produced horizontal lamination by the same principle of 
inducing splitting at right angles to the pressure that 
determines slaty cleavage. 
Why, then, do we find an anticline? Because it so hap- 
pened, as is now shown in the exposure, that the vertical 
limestone band at the sides of the notch disintegrated, but in 
the centre remained but little altered, being probably less in 
the stream of percolation. It therefore formed a support to 
the middle of the shales above it, and they were not pressed 
down nearly as much in the middle as at the sides, where 
they had no solid support. 
Probably if denudation had not removed so much, we 
should have been able to see the curious anomaly of Middle 
Limestone Shales passing conformably up into Rhaetic or 
Lias. 
