480 s. V. WOOD, JTJis-., o:n the newer 



The ridge of chalk shown in these sections is a low part of that 

 rectilinear ridge which, running due east and west, is called, as it 

 rises to greater elevations, the Hogshack, and forms a portion of 

 the escarpment of the Weald. 



Pig. IV., on the true scale, is reduced from a portion of one of 

 the sections given in the Geological Survey Memoir of the Isle of 

 Wight, and shows the position of the South-Hants gravel relatively 

 to the rectilinear chalk ridge which runs through that island and is 

 continued through the Isle of Purbeck. This ridge and that of the 

 Hogshack appear to me, along with Portsdown Hill, to be of distinct 

 origin from the general curvilinear escarpment and foldings of the 

 Chalk throiigh England, which resulted from disturbances at an 

 earlier part of the Tertiary period, and to be due to the movements 

 which accompanied the recovery from the great submergence which 

 I am about to trace. The denudation which accompanied these 

 upthrusts of the chalk, both in North and South Hants, has, it 

 seems to me, removed much of the Lower Tertiary which, covered 

 by h 2, had previously extended with an easier slope over the 

 Chalk as the earlier Tertiary movements and denudation had left it. 

 In one or two places gravel rests on the upturned chalk ; and this 

 seems to me to be a remnant of that which accumulated during the 

 rise which commenced with this disturbance and denudation. 

 In order to show the connexion of the isolated bed of gravel on 

 Headon Hill in this section with the rest of the South Hampshire 

 sheet, I have added another by myself (fig. V.), in which the ver- 

 tical scale is also unavoidably in excess *. 



Under the influence of an elevatory movement in general over 

 England, the local convulsions attending which have thus left their 

 record, the sea-bottom over which the gravel of the great sub- 

 mergence had been spread began to rise. As it did so, the action 

 of the waves removed much (most, indeed) of the gravel, leaving it 

 only in patches of greater or less extent in spots that, from some 

 particular cause or other, were protected from this action, until by 

 their emergence they became entirely free from it. Over the rest 

 of the bottom this action not only removed the gravel, but denuded 

 the older beds also, so as to produce (or probably, over the formations 

 older than the Pliocene, in most cases only to deepen) the troughs, 

 valleys, or depressions which separate these remnants of the gravel 

 at highest elevations from each other. In these denuded spaces 

 gravel again accumulated during pauses in the movement of eleva- 

 tion, which was subjected to the same action in its turn as the 

 gravel before it had been. Where the slope is easy, however, there 

 may have been in some cases no denudation, and the gravel at 

 lower elevations may be that which covered the bottom from the 

 time of greatest submergence onwards till emergence, such as that 

 marked c and « in fig. Y. If so, the gravel e in that figure would 

 represent c and h' also. 



* I have availed myself of the map to Mr. Codrington's paper in Quart. 

 Journ. Geol. Soc. vol. xxvi. p. 628, and the Geological Survey Sheet, in con- 

 structing this section. 



