MINERAL SPRINGS OF GLOUCESTERSHIRE AND WORCESTERSHIRE. 35 



existence of iodine and bromine, not only in the waters of Cheltenham, but also in the 

 greater number of the salt- springs of Great Britain. 



The previous observations in this chapter have shown, that the great subterranean 

 storehouse of the rock salt and brine springs of England, is the red marl or upper member 

 of the New Red Sandstone 1 , which is immediately subjacent to the Lias. (See Map. PI. 29. 

 fig. 1.) Accordingly we find that sea salt is present in still larger quantities in those 

 wells which occur near the western edge of the formation, where the Lias forms only a 

 thin covering above the red marls. At the new spa near Tewkesbury, the water, though 

 very slightly saline near the surface, was found to be much more impregnated with salt as 

 the sinking was carried downwards; and I have no doubt that similar results would follow, 

 by deepening any of the mineral sources which are so numerous in the Vale of Gloucester, 

 those of Walton, the bottom of Church Down Hill, &c, for instance. Even at Chel- 

 tenham, when experimental borings were made to the depth of two hundred and sixty 

 feet below the surface, the water of the lowest stratum of marl or clay was found to be 

 much more highly charged with the common sea salt, and to contain less of the sul- 

 phates, than the existing wells, none of which have been sunk to a greater depth than 

 one hundred and thirty feet. 



These facts can be only accounted for under the supposition, that the source of the 

 saline ingredients of those waters is the Saliferous Red Marl or Keuper, the uppermost 

 strata of which must, from their known inclination, lie at depths of several hundred 

 feet below the town of Cheltenham. (See PI. 29. fig. 1.) If this be the case, and salt 

 water is continually flowing upon the inclined surfaces of these beds, we can readily 

 explain why it occasionally rises to the surface; for being collected in the New Red 

 System at higher levels than the surface of the Vale of Gloucester, it would naturally 

 ascend to the original level by any cracks or openings which might present themselves 

 in the overlying Lias 2 . 



The salt water having thus to rise through various strata of lias shale, loaded with 

 sulphuretof iron, it is to be presumed, that during this passage certain chemical changes 

 take place, which give to the waters their most valuable medicinal qualities. The most 

 important process in this moist subterranean laboratory, is probably the decomposition 

 of the sulphuret of iron, which supplies a large quantity of sulphate of the oxide of iron, 

 an elaboration which must be highly accelerated by the structure of the incoherent and 

 finely laminated beds, through which the pyrites is so widely disseminated. The sul- 

 phuric acid, thus generated, will necessarily react on the different bases, such as mag- 

 nesia and lime, which it may meet with in the strata, and form those sulphates so pre- 



1 See the memoir of Dr. Holland, Geol. Trans., vol. i. p. 38, and that of Mr. L; Horner, vol. vi. p. 95, Old 

 Series ; also the recent work of Dr. Hastings of Worcester. (See p. 32.) 



2 The borings for mineral water at Cheltenham are, truly speaking, Artesian wells, and ought at once to 

 explain to the inhabitants of the Vale of Gloucester, that no pure water can be obtained by sinking through the 

 Lias in the vicinity of the mineral springs. 



