446 A. J. Jukes-Broivne — Boring at Marston, Devizes. 



The Iviiueridge Clay is believed to be about 300 feet tliick at 

 Swindon, and the same thickness is assigned to it in the Index to 

 Sheet 282 of the Geological Survey map, Devizes being about 

 20 miles south of Swindon. In the memoir on the Country around 

 Devizes I did not venture to suggest any thickness for the Kimeridge 

 Clay, of which only a small area comes within the limits of the sheet, 

 and I was not responsible for the Index on the colour-printed 

 edition of 1905, nor for the horizontal section at the foot of 

 that map, which exaggerates the slight syncline that exists below 

 "Wotton and Pottern, and also seems to bring the base of the Kimeridge 

 Clay too near the surface under Seend Hill, probably in order to 

 make the position of its base agree with the assumed thickness of 

 300 feet. 



The village of Marston is about 3 J miles south-west of Devizes, 

 and the site of the boring is at Manor Farm, near the cross-roads, 

 where the level of the ground is marked as 176 feet above O.D. The 

 base of the Portland Sands comes in about three-quarters of a mile to 

 the south-east, at a level of about 210 feet, and as the strata must be 

 nearly horizontal near Marston the top of the boring will be about 

 34 feet below the summit of the Kimeridge Clay. 



The boring had been carried to a depth of 180 feet before I was 

 consulted about the prospect of finding water, and Messrs. J. W. Titt 

 and Co. of Warminster were the engineers and contractors. In 

 advising the continuance of the boring I certainly expected that the 

 base of the Kimeridge Clay would be reached at a less depth than 

 400 feet, and there is every reason to suppose that the underlying 

 Corallian limestones would furnish a plentiful supply of water when 

 they were reached. Unfortunately the Clay has proved to be thicker 

 than was expected, and as there was no sign of nearing its base at 

 400 feet the proprietor could not be induced to proceed farther in 

 the attempt, so that the boring was abandoned at 412 feet.^ 



'No samples were taken from the upper part of the boring down to 

 about 150 feet, and all the information that Messrs. Titt could give 

 me was that the material passed through varied very little and was 

 similar to a sample sent from about 154 feet, which is a sandy grey 

 clay, the sand being of very fine grain. 



Between 154 and 157 feet there seems to have been a bed of very 

 sandy clay or clayey sand, for the sample sent leaves when washed 

 a large residue of sand, which consists almost entirely of quartz- grains, 

 rounded or subangular, partly very small and partly of larger but 

 even-sized grains, with only a few pieces of calcite, which may be 

 worn shell-fragments. No Foraminifera could be seen. Anothei" 

 sample from about 165 feet is a similar dark - grey sandy clay, 

 but between that and 167 feet there seems to have been a bed 

 containing small fragments of stone. The sample yielded a large 

 residue of sand, consisting mainly of subangular quartz-grains 

 varying in size from the finest sand to grains of more than a 

 millimetre in diameter ; in this sand were some fragments of calcite, 



■* The apparent discrepancy between 400 and 412 feet is due to the fact that 

 the Gontractor bored an additional depth of 12 feet at his own cost. 



4 



