of the Eastern and Western Chalk Denudations, 1 69 



ting, indeed, but little in any part of their course ; severally dying 

 out, and their respective synclinal lines playing off into each other. 

 Their course is rather irregular, and their force exceedingly varia- 

 ble ; but their general parallelism is maintained throughout, their 

 progress being E. and W., with a point to the N. 



The Pewsey line, after passing through the valleys of Ham and 

 Kingsclere, is traceable between Woolverton and Hannington, on 

 towards Monks Sherborne, and fades away at Old Basing, apparently 

 without entering the tertiary beds of the London basin *. This 

 meets in synclinal relation with a line projected from the north- 

 west corner of the Wolmar valley from Pease Marsh, near Guildford, 

 through Farnham and the high chalk range of Froyle, Shaldon, 

 Dummer and Popham, and appears to fade away in the country 

 west of Andover, where it is lost in the greater swell of the Bura;h- 

 clere Hills, and the more dominant power of the Pewsey upheaval. 



The anticlinal line of Wardour, left by Dr. Fitton (in his * History 

 of the Beds below the Chalk 'f) at Harnham Hill, S. of Salisbury, 

 Mr. Martin finds traceable eastward, north of Dean Hill, and east of 

 the Avon, to the banks of the Test, where it dips under the tertiary 

 beds between Michaelmarsh and Romsey, and appears to fade away 

 between the above-mentioned river and the Itching. In synclinal 

 relation this line is also met and passed by a very remarkable anti- 

 clinal, traceable in strict approximation with, and by-and-by to be 

 proved to be the proximate cause of, the whole line of the South 

 Down escarpment (with a small exception between Lewes and Poy- 

 nings) from Beachy HezA to East Meon. In the vicinity of this place, 

 at Langrish, it enters the chalk, passes through the anticlinal valley 

 of Chilcomb near "Winchester and that city, and is lost in the Bos- 

 sington Hills, pointing towards, but not satisfactorily traced into, 

 the Warminster line. 



The details of all three lines of elevation are made out in the 

 Ordnance Map, and sections given of the most illustrative points : 

 and Mr. Martin adds some observations respecting the entrance of 

 the great central line of elevation of the Weald into the chalk at 

 Selborne, and its progress westward between the lines of Pease- 

 marsh on the north, and of Greenhurst or the South Down on the 

 south, till it fades away in the great plateau of Salisbury Plain. 



The author concludes this paper with some reference to the sub- 

 ject of transverse fractures in these several longitudinal fissures, and 

 the cross drainage, to which, like that of the Weald, he proposes to 

 return, in extension and emendation of the disquisitions formerly 

 published by him, as above alluded to, and which will be adduced 

 as illustrative of the strong probability, if they do not amount (in 



* The author thinks, that although this line fades away as it enters the 

 tertiary beds at Old Basing, it is probable that, after passing silently along 

 the London basin, it is revived again in the Isle of Thanet, which is a 

 chalk outlier, by protrusion; in the same way that the parallel line of 

 Portsdown Hill, High-down, near Worthing, and the Seaford Cliff (figured 

 by Dr. Mantell) does on the southern coast. 



•f* Geol. Trans., Second Series, vol. iv. p. 244. et seq. 



