STEATA OF THE HAMPSHIEE BASIN. 147 



convincing kind of the correctness of the reading of these sections 

 which I now offer. If, as is supposed by the earlier interpretation, 

 the strata of Colwell and Totland Bays be only a repetition of those 

 of Headon Hill, resulting from the presence of a great anticlinal 

 flexure, then the well-marked white sands of Headon Hill ought to 

 be found near the summit of the anticlinal in Totland Bay. In this 

 position they are actually represented as occurring, in both the 

 longitudinal and vertical sections of the Geological Survey *, it being 

 supposed that they are concealed by heavy masses of talus which 

 cover that portion of the cliffs. Now within the last few years 

 excavations have been made at this locality for the purpose of erect- 

 ing the new reading-roomsj and it is found that the Headon-Hill 

 Sands do not occur in the position indicated by the Geological Survey, 

 but that beds are found which have their exact counterpart in the 

 Headon-Hill section, not at the base, but at a much higher part of 

 the series. I looked forward with great interest to the opening of 

 these sections in Totland Bay, as enabling me to apply a crucial test 

 to the two interpretations of the section ; and the results are such 

 as to remove any possibility of doubt upon the subject. 



Again, the position of the Bembridge Limestone at Headon Hill 

 quite agrees with the interpretation of the section which I now 

 offer, but is altogether irreconcilable with that which has hitherto 

 been adopted. It is admitted on all hands that at the north-east 

 angle of Headon Hill the marine band ("Middle Headon beds") 

 makes its appearance just above the sea-level. Now the excellent 

 maps of the Ordnance Survey enable us to fix with the greatest 

 precision the height above the sea-level of the Bembridge Limestone, 

 which is so well exposed with all its characteristic fossils near the 

 cottage on the Warren. "We thus learn that 250 feet of strata must 

 intervene between the Bembridge Limestone and the marine band 

 of Headon HiU ; but the Geological-Survey section shows less than 

 one half of that thickness of beds, and in Colwell Bay the distance 

 between the Bembridge Limestone and the marine band is 120 feet. 

 Hence, if we believe that the marine bed at Headon Hill is identical 

 with that at Colwell Bay, we must suppose that in a distance of 

 little more than one mile a mass of beds 120 feet thick has expanded 

 to 250 feet, and, further, that the beds have been entirely changed 

 in their mineral characters. But 250 feet of strata is precisely 

 the thickness required by my interpretation. It may be objected 

 that the marine beds of Colwell Bay have never been detected in the 

 upper part of the Headon-Hill section, where they must exist ac- 

 cording to my view. But those who know the manner in which 

 the succession of beds is obscured in the upper part of Headon Hill, 

 through land-slips and the great capping of gravel, will feel Httlo 

 surprise that this particular bed has never been seen there. 



In the two diagrammatic sections on Plate YII. the two readings of 

 the succession of strata, as seen at the western end of the Isle of 

 Wight, are illustrated. Fig. 1 is exactly copied from the diagram 



* Horizontal Sections, sheet 47 ; Vertical Sections, sheet 25. 



