304 MR. H. B. WOODWAED ON A WELL-SINKING AT SWINDON. 



feet. 



Oolites 148 



< Lias and Ehaetic beds 608 



Eed Marls 291 



Eed Sandstone 137 



Coal-measures 225 



1409 



The thickness of the New Eed beds, according to Prof. Hull, 

 diminishes in a south-easterly direction from the Staffordshire area, 

 and he inferred that the Lias would disappear below Oxford*. 

 Mr. Tople}^, moreover, has shown that the attenuation of the 

 Oolites corresponds with the dip, so as to bring the New Eed rocks 

 nearer to the surface in a south-easterly direction from the Cottes- 

 wold outcrop t. 



On the borders of the Bristol Coal-field the thickness of the 

 Secondary strata is much reduced, and the Lias and Ehsetic beds in 

 places overlap the New Eed strata and rest on the older rocks. A 

 short distance west of Bath the Coal-measures come to the surface 

 overlain by the Keuper Marls of very little thickness. Further 

 south, on the eastern end of the Mendip range, near Frome, the 

 Eed beds and Lias are overlapped by the Inferior Oolite, which then 

 rests in places directly on the Carboniferous Limestone. 



The Bristol and Somerset Coal-field is probably bounded on the 

 east by an underground margin of Lower Carboniferous rocks, which 

 would underlie the Lias and Oolites east of Bath ; but the more 

 easterly arrangement of the older rocks is a matter of uncertainty, 

 for near "Wotton Underedge the Eed Marls repose on Silurian 

 rocks. 



In this northern area a mineral water was obtained from a well 

 sunk from 40 to 50 feet deep in the Lias. The locality is Cherry- 

 rock Farm, north-east of Wickwar, and an analysis was published 

 by Mr. T. J. Herapath. The salts present were magnesium sul- 

 phate 129 grains in the imperial gallon, sodium sulphate 122, 

 calcium sulphate 75, calcium carbonate 31, and sodium chloride 60. 

 Mr. Herapath states that most of the springs in the neighbour- 

 hood, when sunk to a great depth, are inclined to be salt J. Here 

 the New Eed strata are comparatively thin, and rest in all pro- 

 bability on the Silurian rocks. 



Again, the thermal springs at Bath and Clifton, which contain, 

 among other ingredients, sodium chloride, and in the former case a 

 large amount of calcium sulphate, rise from the Carboniferous rocks 

 in a district where no rock-salt is known to exist in the New Eed 

 strata §. 



Moreover at Twerton, near Bath, saline waters containing 112*8 



* Quart. Journ, Geol. Soc. vol. xvi. pp. 63, 71 ; see also the Memoir on the 

 Triassic and Permian Eocks of the Midland Counties, 

 t Quart. Journ. Geol. Soc. vol. xxx. p. 186. 

 X Quart. Journ. Chem. Soc. vol. ii. p. 200. 

 § One may neglect the evidence of pseudomorphous crystals of rock-salt. 



