6 ME. Ct. W. LAilPLrGH OX THE JrXCTIOX OF [vol. Ixxviii, 



displayed. The larger masses occurred only under the low dome of 

 unbroken iron-pan (C in fig. 3 of the previous paper) which rises 

 from both sides towards Harris's pit, declining gently northwards 

 and southwards, as shown in fig. 12 (-p. 22). In Chance's pit on the 

 north, the limestone became much streaked and intermingled with 

 glauconite and gi'it, and was usually more or less decomposed, so 

 that its fossils, though readily disentangled, required sizing for 

 theu' preservation ; and in places the I'ock passed into a soft ochreous 

 calcareous paste in which the fossils were obliterated. A large 

 nmnber of the specimens in the TN^alker Collection were obtained 

 from this pit. Similar conditions were also observed on the south 

 as the working in G-arside's pit advanced westwards, the Hmestone 

 decreasing in quantity- until it was reduced to a few soft calcareou.s. 

 patches occuri'ing as matrix am.id the ironstone-breccia. 



It is noteworthy that the cleanest and whitest ' silver sand,' 

 for which the pits are worked, has been found under the dome, 

 where the iron-pan floors are unbroken ; feiTuginous discoloration 

 sets in on both flanks whei*e these bands become lenticular and 

 breccia ted, and where the firm thick tables of limestone are absent.^ 



The clay-cover became steadily thicker as the workings were 

 pushed westwards, and in this cover Harris's pit, now cutting into 

 the steeper clay-slope, has recently disclosed some new information 

 respecting the Gault. From its slippery character the sections 

 in the G-ault are soon spoilt, and need to be seen under favour- 

 able circumstances. Dr. Kitchin ct ]\Ir. Pringle appear to have 

 fomid a clear section in this pit in October 191S, revealing about 

 10 feet of Gault ; but they m.ention that this was obliterated by an 

 extensive slip early in 1919. which, however, enabled them to 

 examine some higher G^ult. estimated to be about 18 feet above 

 the base- : by careful search they obtained some fossils, hitherto 

 uiirecoi*ded, from the sparingly fossiliferous lower portion of the 

 Gnult, together with a few others from higher levels. Last year 

 (1920) a richly fossiliferous band was exposed near the top of the 

 section, and enabled me to collect material which throws light on 

 the relations of the Upper and Lower Gault in the district. 



The section exposed in the northern part of Han-is's pit in the 

 autumn of 1920 is shown in the following figure (fig. 3, p. 7), 

 which maybe compared with the section farther south in the same 

 pit in 1902, given in fig. 3 of our previous paper. 



1 Many particiiLars respecting tlie Leighton Sands from tlie economic stand- 

 point, including descriptions of the "workings and the methods of treatment of 

 the material, -n-ill be found in Mem. Geol. Surv. ■ Special Eeports on the Mineral 

 Resources of Great Britain: vol. vi. Eefractory Materials.' kc. 2nded. (1920) 

 pp. 180-83; and in Prof. P. G. H. BosAvell's = British Eesouxces of Sands 

 suitable for Glass-making. &c.' London. 1916, and ' Supplementary Memoir 

 on British Eesources of Sands & Eocks used in Glass -manufacture. <tc.' 

 London, 1917. 



- Geol. Mag. 1920, p. 9. 



