R. MORTIMER ON A WELL-SECTION IN THE CHALK AT DRIFFIELD. Ill 



7. An Account of a Well-section in the Chalk at the north-end of 

 Driffield, East Yorkshire (supplementing the writer's previous 

 paper*). By B. Mortimer, Esq. (Read March 25, 1874.) 



(Communicated by W. Whitaker, Esq., B.A., F.G.S.) 

 [Abridged.] 



This well was dug in the spring of 1873. The site is on ground at 

 at an elevation of 120 feet above the level of the sea, and slopes 

 gently towards the south. The first 7J feet of the section was 

 through the feather-edge of a bed of clay of late glacial age, in 

 which, at a depth of 6 feet, lay a large and irregularly formed 

 boulder of trap-rock, with angles but slightly worn; there were 

 portions of several other rocks. Under this clay is chalk in a very 

 rubbly and broken-up state, to a depth of from 3 to 4 feet, after 

 which it gradually loses the broken-up appearance, and assumes 

 the horizontal laminated form. The chinks and fissures in the 

 upper portion of the chalk were stained to a depth of 8| feet with 

 argillaceous matter from the percolation of rain-water through the 

 overlying clay ; but beneath this depth there was no colouring- 

 matter visible from above. 



The portion of the section which passed through chalk was 47 

 feet in depth. A careful examination showed that horizontal laminae 

 existed from top to bottom, and varied in thickness from -^ of an 

 inch to 16 inches. Erom a depth of 20 feet to the bottom, the sides 

 of the well exposed mauy nearly vertical partings, or faces, in the 

 chalk, where horizontal striae were beautifully shown, covering several 

 square feet together. One large buttress-formed piece exhibited 

 two sides of a square elaborately filled with horizontal striae. At 

 a point about two thirds of the depth of the well, the face of the 

 chalk showed the same kind of markings, but in this case making 

 an angle of about 45 degrees with the horizon. These striated 

 fissure-like partings in the chalk, many of which appear to have 

 never been firmly united with the mass, ran in all directions. In one 

 place several feet of striae ran from north to south, while above and 

 below these facets pointed in every direction. No appearance of 

 flint was observed. 



Intimately connected with, and spread between the hard chalk 

 laminae were numerous thin horizontal layers of a softer and muddy- 

 coloured substance (fuller's earth), of the consistency of compact 

 clay. This material, varying in thickness from | of an inch down 

 to a mere film (though in some of the chalk-pits in the neighbour- 

 hood it is occasionally from 2 to 3 inches thick), is here found 

 between all the horizontal layers of the chalk. At the depth of 31 

 to 38 feet there are three beds about 3 feet apart, and measuring 

 from | an inch to f of an inch in thickness. This fuller's earth, 

 when first taken from the rock, is of a tenacious nature, but in 

 * Quart. Journ. Geol. Soc. vol. xxix. (1873) p. 417. 



