It. M. Brydone — Further Notes on the Trimmingham Chalk. 77 



flattens out southward to quite a gentle dip over a comparatively 

 ■very extensive area, showing the steep dip to be very local. 

 Probably we have in the bluff of to-day a remnant of the steeply 

 dipping area only of Lyell's bluff, but whether that is so or not 

 Lyell's figure is a very strong argument against assuming the 

 general prevalence of a steep dip at this point. 



The only possible explanation of these local phenomena seems to be 

 one on the lines of the original and ingenious theory of Mr. Clement 

 Eeid, varied by postulating the lateral thrust as of Cretaceous age, 

 directed almost due south and very local, and leaving the thrusting 

 agent altogether indefinite. Except at this very point the thrusting 

 force only created a gentle anticline. This anticline of greatly 

 varying sharpness must have been exposed to denudation, which 

 planed off the upper part and more or less flattened the sides, and the 

 surface so formed was then resubmerged and the grey chalk deposited 

 on it to a minimum thickness of three feet. At some date shortly 

 before the formation of the glacial beds, the chalk must have been 

 again raised and exposed to a south-westerly sea, which formed 

 caves in it which were filled by the first inflow of boulder-clay. 

 The bottoms of these caves are probably well below the present beach 

 level, and we only see horizontal sections through the roofs and the 

 upper surface of the infilling clay, which of course then appears to 

 be underlying the thin edge of the broken-through roof by natural 

 deposition. The detached masses of chalk seen in the cliff behind 

 the bluff have clearly been carried up by a mass of clay from below, 

 and represent parts of the roofs of these caves, which were too weak 

 to resist the upward pressure of the clay. Possibly this upward 

 pressure was applied at a much later date than the infilling of the 

 caves, for the thin line of chalk recorded as connecting two masses 

 of chalk is strongly suggestive of chalk, so to speak, rolled out 

 between the upper and lower clay, and this could only take place by 

 a fresh movement of the lower clay after the upper clay had taken 

 up its present position. It is also suggested by the regular blending 

 of the deposits immediately overlying the chalk just at this point that 

 after the first influx of clay had filled up the sea bed to the level of 

 about the top of the chalk there was an interval, during which the 

 above-mentioned regular deposits were formed on the new sea floor 

 so created, before this sea floor was covered by the upper clay, and 

 then broken up by renewed motion in the lower clay. 



5. Otlier Exposures. 



A new feature of interest is the exposure for a short time of 

 a patch of 0. limata chalk, about 30 yards by 12, some 340 yards to 

 the south of the south bluff, i.e. roughly, intermediate between it 

 and the short ridge exposed some years ago at the foot of the cliff 

 under the brickfield (which latter I will call for convenience the 

 brickfield chalk). This new patch of chalk was practically touching 

 the base of a great mass of firm clay which forms at present tlie 

 first headland to the south of the south bluff, and appeared to pass 



