Geological Society. 215 



clay, at a spot situated within the area of the chalk basin of 

 Newbury, and affording a remarkable exception to the general 

 regularity of that basin. 



This irregularity of structju'e has apparently originated 

 from a sudden elevation of the chalk, accompanied by frac- 

 ture and an inverted dip ; its position is remarkable as being 

 near Inkpen Hill, a point where the chalk rises to 1011 feet, 

 the highest elevation it attains in England. 



In the valley subjacent to the Inkpen ridge, and near its 

 north base, the chalk dips rapidly in two opposite directions, 

 nearly north and south, on each side of a central axis or anti- 

 clinal line ; and a little further east the green sand also emerges 

 with a similar double dip, and forms the small valley of Kings- 

 clere, surrounded on all sides with an inclosing escarpment of 

 chalk. 



The north frontier of this valley is in close contact with well 

 characterized deposits of plastic clay dipping like itself rapidly 

 towards the north. Four similar valleys are adduced in the 

 counties of Wilts and Dorset ; and the author concludes re- 

 specting them all, that it is utterly impossible to explain their 

 origin by denudation alone, nor indeed without referring the 

 present position of their component strata to a force acting 

 from below and elevating the strata along the line of the cen- 

 tral axis of the valleys in question. To valleys of this kind the 

 author applies the appellation of Valleys of Elevation, to distin- 

 guish them from those which owe their origin simply to dilu- 

 vial denudation. He then proceeds to show that the valleys of 

 Pewsey near Devizes, and of the Wily and the Nadder above 

 Salisbury, have also to a certain degree been affected by a force 

 acting from beneath and elevating the strata at a period ante- 

 cedent to their being submitted to denudation; and concludes 

 that not only these inclosed valleys similar to that of Kings- 

 clere, but many open valleys also (though in all cases modified 

 by subsequent denudation), had a prior origin, arising from the 

 fracture and elevation of their component strata. This must 

 liave happened in the case of the weald of Kent and Sussex, 

 inclosed as it is with an escarpment of chalk dipping every 

 where outwards in opposite directions, and sometimes very 

 rapidly along the North and South Downs. 



The author proceeds to illustrate, by the position of the 

 strata of plastic clay in the same district, the important geolo- 

 gical (juestion, — whether the chalk was disposed in its present 

 form of trouglis or basins before or after the deposition of the 

 tertiary formations now inclosed in them; and to show that the 

 j)resent inclination of the strata along the south frontier of the 

 basins of London antl Hants took place since the deposition 



of 



