9:2 



ON THE 



By William Whitaker, B.A., (Lond.) 



Of the Geological Survey of England. 



N 1861 a bed was described,, under the name " Chalk-rock/-' 

 which, in the counties of Wilts, Berks, Bucks, Oxon, and 

 Herts, seemed to form the top of the Lower Chalk. 1 Its occur- 

 rence in the Isle of Wight, though in a less marked form, has since 

 been noticed; 2 some new sections in North Wilts have been described 

 in the Wiltshire Society's Magazine by my friend Mr. T. Codrington, 3 

 and I have also seen it in Bedfordshire 4 and Dorsetshire. As it is 

 open to view near the town (Wilton) where the Society is to hold 

 its meeting this year (1870), a description of two sections in that 

 neighbourhood may perhaps be acceptable. 



The Chalk-rock, where best developped (from near Marlborough to 

 near Henley-on-Thames) is a hard somewhat crystalline cream- 

 coloured chalk, ringing when struck with the hammer, jointed, and 

 with layers of irregular-shaped green-coated nodules. Sometimes 

 however it consists simply of one hard nodular layer. 



In the cutting on the South Western Railway just north-east of 

 Barford St. Mary (west of Salisbury), there is a good thickness of 

 the Upper (or flinty) Chalk, the flint occurring both in the form of 

 nodules and of thin tabular layers. From below this the Lower- 

 Chalk (which here contains a few flints) rises westward at a very 

 small angle : it is hard and of a somewhat nodular structure, and at 

 (or close to) the top has a layer of green-coated nodules. This hard 

 nodular layer is the bed to which I wish to draw attention, not only 



i Quart. Journ, Geol. Soc, vol. xvii, p. 166. See also Geological Survey 

 Memoirs on Sheet 13, p. 19 (1861) and on sheet 7, p. 5 (1864). 



2 Quart. Journ. Geol. Soc., vol. xxi, p. 400. 

 3 Yol. ix, p. 167. 



4 Mr. J. Saunders, whose notice I called to this bed, has described a section 

 near Luton, Geol. Mag., vol. iv, p. 154. 



