266 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 23, 



follow the northern outcrop of this deposit to Woodbridge. Taking 

 a line by Newbury and then northward of Woolhampton to Reading, 

 I know of but one tolerable section of this bed ; it occurs in a brick- 

 field on the summit of the hill at Englefield near Theale*. The 

 London clay caps the hill to the depth of twenty to thirty feet. It 

 is brown and sandy, and contains at its base a band of tabular septaria," 

 very ferruginous and containing a few rounded flint pebbles. These 

 septaria are occasionally full of the casts of the following shells : — 



Cardium. Panopaea intermedia, Sow. 



Calyptraea trochiformis, LamJc. Pectunculus Plumsteadiensis, Sow. 



Ditrupa plana, Sow. sp. Rostellaria Sowerbyi, Mant. 



Nucula ? Soft, brown wood in fragments. 



Natica. Teeth of Lamnae. 



The sands and mottled clays outcrop immediately under these beds, 

 and the chalk appears at the northern base of the hill. 



At Reading Mr. Rolfe has pointed out a thin stratum overlying the 

 Plastic clay series, and containing the following organic remains f: 



Cytherea obliqua, Desk. Ditrupa plana, Sow. sp. 



Pectunculus brevirostris. Sow. Modiola elegans, Sow. 



Natica glaucinoides. Sow. 



In addition to these I have found 



Cardium Plumsteadiense, Sow. Scalaria. 

 nit ens. Sow. Ostrea. 



But by far the best section, and one showing a considerable length 

 of the basement bed of the London clay, was exhibited on the line of 

 the Great "Western Railway at Sonning Hill between Reading and 

 Twyford. The cutting, which is sixty to seventy feet deep and about a 

 mile long, traverses the mottled clays. These are covered in the 

 highest parts of the cutting by three to four feet of brown clay with 

 subordinate and irregular layers of yellow sand, the whole mixed with 

 seams and patches of greensand and with some round flint pebbles. 

 Irregular layers and masses of these materials, cemented by carbonate 

 of lime and full of well-preserved shells, are of common occurrence. 

 (See fig. 12.) A thick bed of ochreous flint gravel caps the section. 



Fig. 12. — Section at Sonning Hill. 



a. Ochreous flint gravel. 



b. Brown London clay, with septaria. 



c. Yellow sand, with irregular seams of brown clay 

 and green sand ; a few round flint pebbles, and 

 numerous tabular calcareous concretions. Fossils 

 dispersed throughout, but peculiarly abundant 

 in the calcareous blocks. Thickness varies from 

 4 to 5 feet. 



d. Upper part of the sands and mottled clays. Sur- 

 face worn and irregular. 



The chalk lies at about 70 to 80 feet below " c," but is not exposed. 



* I have found traces of this stratum at several places on the hills both to the 

 N.E. and S.W. of Theale, but only in small road-side cuttings. 



t Trans. Geol. Soc. 2nd Ser. vol. v. p. 127. The similarity of the organic re- 

 mains of these beds at Reading, Watford, Hampstead, and some other places, has 

 already been pointed out by Mr. John Morris so far back as January 1837 (Proc. 

 Geol. Soc. vol. ii. p. 452). Jn the determination of the fossils of many of these 

 lists I have to express my obligation to Mr. Morris. 



