90 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



high hills at Lane End, four miles west from High Wycombe. The 

 summit of this hill consists of London clay with a thin layer of the 

 " Basement Bed," with its characteristic fossils beneath it ; this is 

 succeeded by sands and mottled and laminated clays reposing upon 

 the chalk. Sands predominate, and no fossils have been found. 



On the chalk hills around Missenden, Amersham, and the Chal- 

 fonts, traces of the lower tertiaries frequently occur, but they are 

 so covered and mixed with drift that it is rarely that clear sections 

 can be obtained. One and a half mile east from Chesham is Tiler's 

 Hill, where again we find, at a distance of nine miles north of the 

 main mass of the tertiaries, an outlier of London clay reposing upon 

 the lower tertiaries. 



The falling in of the shaft of a chalk-pit has recently (1853) as- 

 sisted in exposing a complete section of this hill from the London 

 Clay down to the Chalk. Though not very accessible, it shows a 

 clear unbroken sequence, and affords therefore a good key-section. 



Tiler's Hill, Chesham {section from sand-pit and shaft of chalk-pit 

 in the brick-field). PI. I. Diag. B, Loc. sect. 1. 



Feet. 

 Gravel, chiefly of flint-pebbles in clay, averages 4 



London Clay. < 



Basement-bed 

 of the London « 

 Clay, Z\feet. 



11. Woolwich and 



Brown clay with a few nodular septaria 10 



Layers of laminated grey and brown clay 3 



Layer of imperfect septaria full of fossils* 0^ 



b. Light brown sandy clay 2 



a. Flint-pebbles in clay 1 



h. Umber-coloured clay, in places slightly mottled red 



and yellow 2 



g. Fine siliceous sand, in places very white 3 



f. Light-coloured soft sandstone with an occasional 



pebble — variable 1 



rr uyi^ii,,,. u.,iu, j ^^ Light-coloured siliceous sands with a few seams of 



^y^ff '1 grey clay, the lower part coarser, yellow, and brown 10 



^ ' d. Laminated grey and yellow clay and sand, with an 



under-seam of pebbles 1 



e. Yellow and ash-coloured sand with seams of grey clay 8 



b. Grey clay laminated with sand -4 



a. Large unrolled flints, apparently white-coated 2 



51A 

 Chalk 25 



It is to be observed that here a layer of the sand passes in places 

 occasionally into soft sandstone. 



Returning soutliAvard we fall in with the main body of the tertiaries 

 near Beaconsfield. In a section at Pitlands Wood, one and a half 

 mile east of this village, thin patches of subangular flints occur 

 apparently beneath the mottled clays. From Starveall to Hedgerley 

 is a succession of sections which are interesting from their exhibiting 

 the very rapid structural changes which take place in these sands and 

 mottled clays. 



The two local sections, 12 and 13, in Plate L Diag. A, are actual 



* The Ditrupa plana abounds, together with Ostrea Bcllovacina, a few Natica 

 fflaucinoides, a Fusus, and teeth of Lamna. 



