The Phosphatic Chalks of Winterbourne and Boxford (Berkshire)

Abstract

I. Introduction. In the latter part of July 1905 we remarked, among the fossils exhibited in the recently-founded Museum at the Cloth Hall, Newbury, a group of guards of the belemnoid Actinocamax granulatus (Blainville), labelled ‘Winterbourne’—the name of a village 3 1/2 miles to the north-west of the above-named town. To us, these specimens were objects of more than usual interest, inasmuch as our examination of the Upper Chalk in the western part of the London Tertiary Basin, so far as it then extended, had shown us (1) that Actinocamax granulatus was a rare fossil in that area; (2) that it was there confined to beds of the Marsupites -Band and of later age; and (3) that such beds, although well-developed to the south of the Kennet, were cut out, by the Eocene overstep, to the north of that river, along a line passing 2 or 3 miles south of the parish of Winterbourne. Assuming the guards to be correctly labelled, they seemed to indicate the existence of an outlying mass of Marsupites -, or newer, Chalk rather rich in belemnoids, within a tract of country where the Eocene deposits were known to be generally in contact with some part of the older, Micraster cor-anguinum - Chalk; and as we had but recently given some attention to just such a mass in the shape of the Phosphatic Chalk of Taplow, the possibility of the recurrence of phosphatic conditions near Newbury at once presented itself to our minds. On our making