284 Eeporfs and Proceedings — Geological Society of London. 



a species comparable witli CUmacograptus confertus. These forms 

 indicate that both the black and the pale shales belong to horizons 

 in the Upper Arenig rocks (Lower Llanviru of Hicks). 



3. " The Phosphatic Chalks of Winterbourne and Boxford 

 (Berkshire)." By Harold J. Osborne White, F.G.S., and Llewellyn 

 Treacher, F.G.S. 



Data collected in the district dealt with in this paper suffice to 

 show that the more or less Phosphatic Chalks above the Uintacrinus- 

 band lie in a trough or basin, the formation of which antedates the 

 deposition of the Reading Beds. When the ai'ea of observation is 

 extended, it is found that the Uintacrinus Chalk of that tract itself 

 lies in a structural depression. In view of the development of 

 phosphatic and of hard, rocky beds, indicative of slow and inter- 

 rupted sedimentation, in the underlying cor-anguinum zone, it seems 

 not unlikely that this basin is an original or inherent feature of the 

 Ohalk directly attributable to a local attenuation of that zone ; but 

 the authors believe the depression to be due mainly to differential 

 earth movements, of which there are many indications. The 

 exposures are found in the eastern (Winterbourne) and western 

 (Boxford) sides of a spur lying in the angle between the converging 

 valleys of the Lambourn and the Winterbourne. On the eastern 

 side the following succession is recognized : — 



1 . Reading Beds of the Borough Hill outlier. 



2. Chalk with some Hints. l Zone of Actinocamax 



3. Phosphatic Chalk. j quadratus. 



4. PhosjAatic Chalk ,f «f^"i''^'^^-t'^°J- Zone of itf^r.^^pi^.s. 



0. Very feehly phosphatic Chalk. Uintacrmus-\is.\i.^. ) ^ 



6. Chalk with tabular flints. \ Zone of Micraster cor- 



7. Chalk with flints. ( anguinum. 



and on the western side — 



1. Reading Beds. 



2. Phosphatic Chalk. Zoneoi A. quadratus. 



3. Phosphatic Chalk. Jifarsiipites-hand. ) 7 f -.^ ., 



4. Feebly phosphatic to normal Chalk. Umtacrinus-baHd. ] ^^"^^ °^ ^"' ^"P'^^^' 

 0. Normal flinty Chalk. 



6. Phosphatic Chalk. i „ r ,r• 

 7. Normal flinty Chalk. ^ZoneoiMxcrastereor. 



8. Pho-sphatic Chalk. ( ««^«"^'""- 



9. Normal flinty Chalk. ) 



The maximum thickness of the Phosphatic Chalk Series is about 

 130 feet. Detailed accounts of the various exposures are given, as 

 also lists of ibssils from the various bands, and an account of the 

 microscopic features of washed residue from the softer chalks of the 

 pit a quarter of a mile north-west of Winterbourne Church. This 

 yields: (1) pieces of Lioceramus shell, the majority unphosphatized; 

 (2) foraminifera, frequently phosphatized ; (3) angular chips of 

 scales, bones, and teeth of fishes ; (4) irregular, angular, or sub- 

 angular lumps and platy pieces of calcite, probably in the main 

 fragments of oysters ; (5) rod-like objects, smooth, cylindrical, or 

 tapered — probably spines of echiuoids ; (6) coprolites of small 



