214 H. L. Hawkins — The A. quadratiis Zone near InJcpen. 



as recently adopted by Kidston and Jongmans.^ All of these sub- 

 medullary types I now regard as, strictly speaking, indeterminable 

 specifically. If any one of them has any claim to be recognized, 

 despite the absence of infranodal scars, it is C approximatiis, Brongn. 



iv. notk on the occurrence of the zone of a. quadratvs 



(Sub-zone of Offaster pilula) near Inkpen, Berks. 



By Herbert L. Hawkins, M.Sc, F.G.S., Lecturer in Geology, University 



College, Reading. 



ALONG the narrow belt of Upper Chalk that forms the northern 

 margin of the Yale of Ham (or Shalbourue), a sunken and 

 picturesque lane passes from the village of Inkpen in a direct line to 

 Shalbourne. At a distance of about a quarter of a mile west of the 

 cross-roads in the village (and about the same north-west of the 

 church), the 500 ft. contour crosses this road. On the new series Survey 

 map (Sheet 267) a quarry is marked on the northern side of the- road 

 near this point, and a northerly dip of 25° is recorded. The quarry is 

 now almost completely grassed over, but about 100 yards to the east 

 of it (practically on the line of the shaft of the arrow on the map) 

 there is an open road-cutting, giving access to the Chalk, on both 

 sides of the road. 



The Chalk is much crushed, and full of small dislocations, but the 

 northerly dip is still quite clear. A few scattered flints occur in it, 

 but no continuous layers. Fossils are exceedingly scarce — indeed, 

 I have paid several visits to the exposure and hitherto failed to find 

 anything zoually distinctive. All organic remains are either already 

 in fragments, or collapse at anj^ attempt to extract them. 



A recent visit to this unpromising section has, however, yielded 

 evidence of considerable interest. In a block of the Chalk that had, 

 for some local reason, escaped the worst degree of compression, three 

 fossils occurred, which, though fragmentary and friable, are unmis- 

 takable. They are Offaster pilula (a small form, just like those from 

 Kintbury, 2J miles to the north-east) ; a very small, pyramidal, flat- 

 based Echinocorys, whose proportions, so far as they can be determined, 

 are exactly those of forms from the 0. pilula sub-zone ; and a primary 

 interradial of Stauranderastei- hilhiferun, which is fully as large as 

 the Offaster. Spencer has shown that this species attains its maximum 

 size in the sub-zone of 0. pilula. Such an assemblage admits of but 

 one interpretation. The sub-zone of 0. J!>«7m/« is here present. The 

 fossils came from the section on the south side of the road, and, 

 though absolutely no traces of fossils have as yet appeared on the 

 northern side, there can be no doubt that the whole cutting is made 

 in this sub-zone. 



According to the geological map, the section occurs about midway 

 between the Chalk Rock and the Tertiarj' border, so that, unless 

 a strike-fault occurs to the north of the road (which is quite possible), 

 there must be a very considerable thickness of the qiiadratus-zoue 

 developed. 



' Kidston & Jongmans, Mededeel. lUjksopspor. Delfstoff, No. 7, vol. i, pt. i, 

 p. 101, 1915-17. 



