454 T. K. JONES AND C. C. KING ON SOME 



but about 18 feet below it in Section No. 4, where they are seen to 

 have a thickness of little more than 18 feet, while they are nearly 

 30 feet thick in Section No 6, 72 yards to the W. They therefore 

 suffered considerable denudation eastward before the Mottled Clay 

 was laid upon them. They show a greater thickness in this locality * 

 than in any other Section in the neighbourhood. The same thick- 

 ness of " Beading Tertiaries," however, as a whole 47' 6", has been 

 measured at Katesgrovef ; but they have much more frequent alter- 

 nations of sands and clays, as observed by Dr. Buckland (' Mem. 

 Geol. Surv.' vol. iv. p. 188). 



§ IV. The Mottled Clays.— The Mottled Clays overlying the Buff 

 Sands just described, and having the same dip, thicken towards the 

 east (in the direction the Sands below thin away) not only in 

 Collier's pit, but in "Wheeler's, on the other side of the hill ; and 

 over the valley beyond, at Katesgrove, as is well known, the 

 ' 'Basement Bed" of the London Clay sets in upon them (Mem. 

 Geol. Surv. vol. iv. p. 188). On the north side of Coley Hill, not 

 only does the westerly thinning-out of the " Mottled Clays (Sec- 

 tions Nos. 1 «fc 6) deprive the occupier of much plastic material J, 

 but a small E.-W. fault at the S.W. corner of the pit still further 

 deteriorates the clay by disturbing and muddling it with the super- 

 ficial gravel; and the little E.-W. fault at the N.W. corner (Sec- 

 tion No. 6) does not let down the clay in sufficient quantity for 

 working. 



In Section No. 5, both the gravel and the Mottled Clay, which 

 shows a slight dip to the S.S.E., thin out on the southern slope of 

 the valley dividing Coley Hill from Castle Hill. The softening of 

 the clay on the slope has given it the appearance of bent laminae 

 hanging over towards the valley. 



§Y. The Superficial Gravel. — In Coley Hill red loamy gravel, 

 chiefly of flint, with some quartz, quartzite, <fcc, overlies the Mottled 

 Clay along a horizontal surface, which, however, has been cut into 

 by the existing valleys. The gravel averages 5 feet in thickness, 

 but is pocketed in the eroded surface of the clay ; and the process of 

 clearing it off, in baring the clay and freeing it from stones, leaves 

 very numerous, close-set, funnel-shaped pits, varying in size, but 

 often nearly 2 feet deep, and 2 or 3 feet across. At both faults, 

 one at the S.W. and the other at the N.^V. corner of Collier's pit, 

 the gravel is deeper. 



§ YI. Theoretical Conclusions. — In conclusion, we wish to draw 



* See also Buckland quoted by Prestwich, Quart. Journ. Geol. Soc.x. pp. 87, 88. 



t Only 38 feet of the Eeading beds, from the Chalk upwards, were seen at 

 the Eailway-cutting, and 33 feet at Castle Kiln. At Shew Hill, near Newbury, 

 Mr. Prestwich measured 52 feet of these strata, the Mottled Clay being 26 feet 

 thick, and having only one seam of sand in it. Many other sections (Sonning, 

 &c.) may be compared in Mr. Prestwich's paper, and in the 'Mem. Geol. 

 Surv.' vol. iv. The irregularity of deposition in the " Reading Beds" has been 

 fully noticed by Buckland, Prestwich, and Whitaker, and is evident in all the 

 Sections ; but in this paper attention is especially directed to the evidences of 

 denudation and reconstruction. 



| At first he supposed that it lay equally over the property. 



