1850.] PRESTWICH ON THE LOWER TERTIARY STRATA. 267 



Organic remains of stratum " c," at Sonning Hill. 



Astarte. Nncula. 



Calyptrffia trochiformis, Lamk. Ostrea pulchra, Sow. 



Cardium Plumsteadiense, Sow. Panopaea intermedia, Sow. 



nitens, Sow. Pectunculus brevirostris, Sow. 



, n. sp. a. Plumsteadiensis, Sow. 



Cytlierea obliqua, Besh. Pleurotoma. 



■ ovalis, var. ? Sow. Rostellaria Sowerbyi, Mant. 



Ditrupa plana, Sow. sp. , n. sp. a. 



Fusus. Scalaria. 



Modiola elegans, Sow. Venericardia ? 



depressa, Sow. Voluta denudata ? Sow. 



Natica glaucinoides, Sow. Spatangus. 



• Hantoniensis, Pilk. Teeth of Lamnae. 



The Ditrupa plana, Cardium n. sp., Cytherea obliqua, Modiola 

 elegans, Natica glaucinoides, Ostrea pulchra, Pectunculus brevi- 

 rostris, and the teeth of Lamnce, were here particularly abundant. 



The more hilly character of the country, and the slight dip of the 

 strata, now cause the outcrop of this bed to expand over a wider area, 

 and to take a very irregular line, which can only be followed at intervals. 



At Holywell near Maidenhead a group of fossils from a bed of 

 this age was described by Mr. Warburton* in 1 821 . These fossils are 

 now in the museum of the Society, and consist of the following species : 



Calyptraea trochiformis, Lamk. Natica glaucinoides ?, Sow. 



Cardium nitens, Sow. Panopsea intermedia, Sow. 



Plumsteadiense, Sow. Pecten. 



Cyprina or Cytherea. Pectunculus Plumsteadiensis, Sow. 



Ditrupa plana. Sow. sp. Pleurotoma. 



Fusus. Tellina. 



Modiola elegans, Sow. Teeth of Lamnae. 



In the midst of the chalk district and nearly ten miles to the north 

 of the main body of the tertiaries, I have met with a well-cha- 

 racterized outlier of the basement bed, underlying a capping of 

 London clay, forming the high hill at Lane End four miles west of 

 Wycombe. I found the fossils in blocks of very ferruginous septaria 

 in some small shallow pits on Lane End Common. They were in 

 the state of casts and impressions, and were extremely abundant in 

 some places. They consist of the following species : — 



Cardium nitens, Sow. Modiola elegans ? Sow. 



, n. sp. a. Natica glaucinoides. Sow. 



Cytherea obliqua, Desh. Pectunculus Plumsteadiensis, Sow. 



Calyptraea trochiformis, Lamk. Teeth of Lamnae. 



Fusus. 



No good section is exposed. 



Another small but interesting outlier occurs on the chalk at Tilers' 

 Hill, one and a half mile east of Chesham. Several brick -pits are 

 worked on the summit of this hill, exhibiting in a series of clear sec- 

 tions the several beds from the chalk to the London clay, which 

 here consists of a brown clay with large septaria. At the base of 

 the London clay is a layer of one to two feet of rounded flint pebbles 

 in sand and clay. To this succeeds a series of sands, with some 

 pebble beds, reposing on the chalk. (The section of this hill will be 



* Trans. Geol. Soc. 2nd Ser. vol. i. p. 52. 



