520 MESSES. WHITE AND TEEACHEE ON THE [Aug. I906, 



(w) Pit at Westbrook Farm. 



This is in normal Chalk, rich in flints but very poor in fossils, 

 and having the appearance of that particularly-uninteresting rock 

 which is usually found in the midst of the Micraster cor-anguinum- 

 Zone in this district. The pit is mentioned, because it shows the 

 beds at that spot to be dipping in the same direction as those 

 in the Boxford Quarry (u), a third of a mile to the south-east, but 

 at an angle of only 5° or 6°. 



The descending succession recognized on the western, or Boxford, 

 side of the Borough-Hill ridge is, then, as follows : — 



1. Eeading Beds of the Borough-Hill Outlier. 



2. Phosphatic Chalk ; exposures k, 1, j, o, p, q? Zone of Act. quadratus. 



3. Phosphatic Chalk ; exposures m, o, p j M ™^ tes ~ j | gj 



4. Feebly-phosphatic to normal Chalk, with few \ JJintacrinus- | H. o 



Hints ; exposures f, h, i, n, o, p, r, S, t ... J Band. ] it "* 



5. Normal flinty Chalk; exposures g, h., i ^ 



6. Phosphatic Chalk ; pit u I „ c tt- 



7. Normal flinty Chalk ; pit u [ Zone ot Mteraster 



8. Phosphatic Chalk (? with flints) ; exposure V j ^r-angumum. 



9. Normal flinty Chalk ; pit W J 



The maximum thickness of the Phosphatic Series, from the base 

 of the beds numbered (8) to the summit of those numbered (2), in 

 the above succession, we roughly estimate at 130 feet ; assigning 

 to the 



Feet. 



Aetinocamax-quadratus Beds 20 



to the Marsupitcs-Zone 30 to 40 



and to the Micraster cor-anguinum-Beds 80 to 70 



IV. Concluding; Eemaeks. 



The data collected in the piece of country dealt with in this 

 paper suffice to show that the more or less Phosphatic Chalks above 

 the Uintacrinus-Band between the villages of Winterbourne and 

 Boxford lie in a trough or basin the formation of which antedates 

 the deposition of the Beading Beds (see fig. 4, p. 510). When the 

 area 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 interrupted sedimentation, in the 

 underlying cor-anguinum-Zone, it seems not unlikely that this basin 

 is an original, or inherent, feature of the Chalk, directly attributable 

 to a local attenuation of that zone. That this explanation contains 

 some elements of truth we do not doubt, but the unusually pro- 

 nounced dips noticeable in the larger excavations in the district, 

 and, above all, the remarkable disturbance which has tilted the 

 Chalk near Boxford at an angle of 25°, strongly suggest that the 

 troughing which sheltered the outlier of phosphatic and normal 



