Vol. 6$.~] THE MOTION OF SUB-SURFACE WATER. 103 



Chalgrave, Todditigton, Shitlington, and Stondon ; while, in the 

 latter county, the sub-surface water-contours in the area to the 

 north and west of Marlborough have their axes parallel to the line 

 of outcrop of the Gault-Clay, which ranges by the foot of the Chalk- 

 hills through Compton Basset, Clyffe Pypard, Wroughton, and 

 Bishopstone. A similar parallelism can also be traced in the north- 

 western extremity of the Salisbury-Plain area : the Contour-lines 

 being roughly parallel to the line of outcrop of the Gault-Clay, 

 ranging by Dilton Marsh and Coulston. 



Finally, if the homogeneous stratum be replaced by one of 

 varying texture and porosity, then the contour-lines, while still 

 retaining a rough parallelism, will be indented or prolonged to a 

 degree proportional to the structural variation of the strata in that 

 locality. If, on the other hand, it be faulted, the faults may 

 either tend to lower locally the water-level by providing freer 

 outlets along the lines of rupture, or else raise it by interposing 

 a more or less efficient dam across the line of flow ; as in the 

 instances previously quoted, the percentage-porosity of a porous 

 stratum may be locally affected by the faulting. It is thus possible, 

 by a careful study of the hydrological map of a district which has 

 been surveyed with some exactitude, to gain a considerable know- 

 ledge of the details of the geological structure of that district 

 which might not be otherwise available, while, at the same time, 

 affording valuable data for the scientific solution of the water- 

 supply and other water-problems of that district. 



V. Bibliography. 



1. W. Boyd Dawktns. 'On the Relation of Geology to Engineering' [James- 



Forrest Lecture] Min. Proc. Inst. C. E. vol. cxxxiv (1898) pp. 255 et seqq. 



2. W. Bland. ' On the Influence of Season over the Depth of Water in Wells ' 



Proc. Geol. Soc. vol. i (1831) pp. 339-40; also Phil. Mag. & Ann. Phil. n. s. 

 vol. xi (1832) pp. 88-96. 



3. W. Boyd Dawkins. Op. supra cit. Min. Proc. Inst. C. E. vol. cxxxiv (1898) 



p. 260. 



4. I. Roberts. ' On the Wells & Water of Liverpool ' Proc. Liverpool Geol. 



Soc. 1868-1869, pp. 84-97; also liep. Brit. Assoc. 1883 (Southport) p. 405 ; 

 and C. E. De Rance. ' The Water-Supply of England & Wales ' p. 17 

 (London, 1882). 



5. H. Daect. ' Les Fontaines publiques de la Ville de Lyon ' Paris, 1856. 



6. — Hagen. ' Handbuch der Wasserbaukunst ' Berlin, 1869. 



7. F. Seelheim. ' Methoden zur Bestimmung der Durchlassigkeit des Bodens ' 



Zeitschr. fur Analytische Chemie, vol. xix (1880) pp. 387-418. 



8. Allen Hazen. Report of the Massachusetts State Board of Health, 1892, p. 541. 



9. C. H. Wolff. ' Water ' vol. viii (1906) p. 134. 



10. C. S. Slichtee. 'The Motions of Underground Waters' Bull. No. 67, U.S. 



Geol. Surv. Water-Supply & Irrig. Papers, 1902. 



11. F. H. King. 19th Annual Report U. S. Geol. Surv. 1898-99, pt. ii, p. 59. 



12. C. C. Mooee. Proc. Liverpool Geol. Soc. vol. xi, pt. ii (1902) pp. 133 et seqq. 



13. Report of the Royal Commission on the Stone to be used for the Houses of 



Parliament, 1839. 



14. B. Latham. Brit. Assoc. Rep. 1881 (York) p. 614, and 1883 (Southport) 



p. 495 ; and ' Croydon Bourne-Flows ' Proc. & Trans. Croydon Nat. Hist. 

 Soc. 1904 ["Special Supplem. 44 pp.] 



15. K. Honda. ' Water,' vol. vii (1905) p. 238. 



16. M. D. Pantanelli. Ibid. vol. vi (1904) p. 37. 



17. F. Wetde. Ibid. p. 151. 



