40 ME. A. M. DAVIES ON THE EIMERIDGE CLAY [Feb. I907, 



where, just below the crest of the escarpment, large Gryphaeas are 

 thrown out abundantly from the ditches. The precise relation of 

 the Arngrove Stone to the Oxford Clay is shown by the following 

 well-section, noted in September 1899. The exact site of the 

 well is at the northern end of Studley village, by the side of the 

 road to Boarstall, close to the 317-point on 6-inch sheet No. 26 

 (Buckinghamshire). The measurements are approximate, having 

 been made by reference to the rungs of a ladder in the well : — 



Feet. 



5. Soil and Arngrove Stone-rubble (outside the well) 3 



4. Arngrove Stone 2 



3. Reddish-brown sandy clay : fish-tooth, Alectryonia- 



fragments, traces of other shells 3 



2. Argillaceous limestone less than 1 



1. Clay, very black and stiff: Gryphcea dilatata, Cardio- 



ceras cordatum at least 10 



19 



From Studley, for more than 3 miles in a north-easterly direction, 

 the Arngrove Stone forms a well-marked escarpment. This dies 

 away rather suddenly at the main road from Oakley to Bicester, the 

 last place where the Stone can be found being on a piece of waste 

 ground on the north-east side of this road. All along this distance, 

 for a varying breadth along the dip-slope, the chert is abundantly 

 exposed in small diggings and in the soil of ploughed fields. Near 

 Studley it is found on both sides of the Danes Brook, which trenches 

 the dip-slope in the direction of the strike. So far, the well-defined 

 boundary-line shown on the geological map between Oxford Clay 

 and Lower Calcareous Grit is quite justified. But, farther to the 

 east, all trace of the chert is quickly lost; and it is difficult to 

 understand the grounds upon which the definite boundary-line has 

 been continued up the valley to Boarstall, and again through 

 Shabbington Wood and along the western side of the next valley, 

 where only a broken line is drawn on its eastern side. Along the 

 north side of Shabbington Wood, the soil is equally clayey on both 

 sides of the mapped boundary-line ; and at one point, a little north- 

 west of Shabbington- Wood Lodge, well within the area mapped as 

 ' Lower Calcareous Grit,' a pond-digging shows clay with abundant 

 large specimens of Gryphcea dilatata and Alectryonia yregaria. My 

 own conclusions as to the extension of the Arngrove Stone are 

 indicated in the sketch-map (fig. 2, p. 41). 



On the south-west, the continuation of the chert is abruptty 

 cut off by denudation. Two miles away, across the broad valley of 

 the Holton Brook and its tributaries, stand the normal Corallian 

 rocks of Stanton St. John ; and it is natural to enquire whether any 

 trace of the Arngrove Stone may be found intercalated in this series. 



