400 GEOLOGY OF THE SOUTH EAST OF DORSETSHIRE. 



mulation. Take the case of Farnborough for instance (fig. R). 



Marrant's Hill. Farnborough. 



R ^T~-— ^ . J> Bromley. 



The pebbles are there found over the chalk, just at its outcrop 

 from under the tertiary beds that extend thence to London. 

 And it will be found, in the generality of cases, that the ac- 

 cumulation has taken place, not at a distance from what must 

 have been the shore of the tertiary sea, but on the very limits 

 of its margin, as defined by the rise of the sloping chalk from 

 under the horizontal layers of the tertiary beds. 



Now, in the case of Studland, the conglomerate with peb- 

 bles is found exactly at the edge of the basin in the slope of 

 the lofty chalk range of Ballard Down, just where the plastic 

 clay series commences ; so is it at Lulworth, for it is at the 

 foot of the Purbeck downs that the pebbles make their ap- 

 pearance. But I am bound to admit, that two lines of these 

 pebbles, regularly imbedded, occur in the sand at Booker's 

 Hill, Lytchett, at a much higher level above the present sea, 

 than that at Studland, — and the difference of elevation is pro- 

 bably 200 or 300 feet ; of which a similar example is afforded 

 at Hinton Martell, where the pebble-bed is found on the sum- 

 mit of a high chalk ridge, whilst the lower lands, also cover- 

 ing the chalk, have traces of these pebbles. 



Here there seems a discrepancy, for if these pebbles mark 

 an ancient littoral accumulation, the tertiary sea must have 

 stood, in different places of the same geological area, at dif- 

 ferent elevations ! But to explain this impossibility we have 

 two solutions at hand. The plastic clay series in south-east 

 Dorset, has experienced enormous dislocation and denuda- 

 tion ; and it is not only probable, but proveable, that there 

 have been depressions and elevations throughout this area. — 

 Moreover, evidence will be advanced in the course of these 

 illustrations, to show that during the deposition of the plastic 

 clay beds, violent denuding and destructive agencies were at 

 work, and that the first-deposited beds were in some cases, as 

 at Wareham, and near the station-house, Studland, broken up 

 to form the constituent portions of a later part of the deposit. 

 So that the ancient shingle of the plastic clay may have been 

 removed and re-accumulated upon other spots, which were 

 then emerging from the general low level to a higher one, un- 

 under the influence of those up-lifting agencies which we have 



