DISTURBANCES AND FAULTS. 243 



the broad flattened syncline occupied by the Hamstead Beds. 

 On the north side of this trough the strata rise at a gentle 

 angle — probably never more than 5°. On the south they rise 

 abruptly at a high angle, so that near the Chalk they are 

 nearly always vertical, sometimes even slightly inverted. Other 

 minor folds occur, but these are all of comparatively slight 

 importance. 



It hiis already been pointed out that the anticlinal and synclinal 

 folds in the south of England form ovals elongated in an east and 

 west direction. This syncline is no exception to the rule, for if 

 the base of the Hamstead Beds be followed by means of wells 

 and borings, it is found to lie below the sea-level for about 14 

 or 15 miles, but then to rise rapidly towards the east, so that the 

 Bembridge Limestone lies at or close to the beach on the coast. 

 On the west the syncline must die out rapidly beneath the Solent, 

 for neither Hamstead nor Bembridge Beds have yet been detected 

 on the mainland, though the bottom of the Hamstead Beds 

 descends well beneath the sea-level at Hamstead and Bouldnor. 



Owing to the absence of any hard rocks in the greater part 

 of the Oligocene series the exact position of the synclinal axis 

 cannot be easily traced, but the various trial-borings made during 

 the progress of the Survey enables us to fix it within narrow 

 limits. Its centre follows a curved line passing through Bouldnor 

 Cliff, Shalfleet, the southern part of Parkhurst Forest, Dorehill, 

 Ashey, Kicketshill, and Brading Harbour. 



On the northern side of this syncline traces of several minor 

 undulations may be detected, but it is difficult to reduce them to any 

 definite system. Headon Beds are brought up near Norris and 

 Osborne in a rather peculiar manner, but this seems to be mainly 

 due to the increase in the rapidity of the dip along a line parallel 

 with tlie coast between Osborne and Ryde. The occurrence of 

 the Bracklesham Beds on the opposite coast shows that such an 

 increase must take place, while at Norris the coast projects some- 

 what beyond the general line, so that the strata are there brought 

 within the influence of this increased dip. 



In Thorness Bay the Bembridge Limestone sinks beneath the 

 sea-level, so that Hamstead Beds are seen in the cliffs. In 

 Newtown Bay, on the other hand, the Osborne Beds rise. These 

 two folds show a tendency to follow east and west lines, but 

 nothing more can be said about them. 



Following next the southern margin of the Tertiary basin, we 

 find that in Whitecliff" Bay, while all the lower beds are vertical, 

 the Bembridge Limestone, after dipping at a very high angle in 

 the upper part of the cliff, suddenly flattens into a horizontal reef 

 on the foreshore, the Bembridge Marls being only slightly 

 affected. This structure continues as far as Brading, where not 

 only is the Bembridge Marl 30*601 ed, but the lower part of the 

 Hamstead series is also tilted slightly. Near Nunwell and Ashey 

 the pressure of the terrestial movement that plicated the strata 

 seems to have reached its maximum, for all the beds as high as 

 the Lower Hamstead series are tilted at high angles and so 



Q 2 



