TUFA. 535 



The tufa sometimes contains much earthy and sandy matter, and 

 is often of a loose and friable nature, but sometimes, as near 

 Dursley, in Gloucestershire, and near Matlock, it forms a hard and 

 durable rock fit for building-purposes. Portions of old Berkeley 

 Castle were built of Tufa from Dursley.^ 



Petrifying springs occur at Chalford near Stroud, Somerton on 

 the Cherwell, North Ashton, Marston Lane near Oxford, at Chilton 

 and other places in Somersetshire, at Matlock, at Alwalton Lynch 

 near Peterborough, Stony Stratford, etc. The Dropping Well at 

 Knaresborough is well known.- The deposit of tufa is made to 

 form more rapidly by the water falling in spray on the objects to 

 be incrusted, and among these birds-nests and flowers are favourite 

 materials. 



Tufa, derived from the Carboniferous Limestone, has been met 

 with near Caerwys and PwU Gwyn, also near Hawarden, in Flint- 

 shire,^ at Prestatyn near Rhyl, and near Llangollen and Wrexham. 

 It occurs near Spouthouse farm and at Southstone Rock, near 

 Tenbury; at Portland;* at Tolland's Bay in the Isle of Wight ; at' 

 East JMalling and Boxley Abbey in Kent; and at Osbournby, in 

 Lincolnshire. 



Mineral Springs are of very varied nature ; in fact there is an 

 imperceptible gradation from waters whose mineral constituents 

 do not unfit them for ordinary drinking purposes, to those which - 

 are highly charged with saline matter. When of Therapeutic value, 

 they are Medicinal Springs, but this term has been indiscriminately 

 applied. The term 'Spa' is often given to mineral springs, and 

 takes its name from the town of Spa in Liege, at one time a place 

 of great resort. 



For more than three hundred years the medical properties of mineral waters 

 have attracted the attention of the learned ; but towards the middle and close 

 of the last century, and for the first twenty-five years in this, there was a sort of 

 rage for these waters. In hundreds of places in this country, where there had been 

 detected waters containing a small percentage of iron -oxide, or saline matter, 

 or which were seasoned with sulphur, there were advertised the virtues of a Spa. 

 At many of these places baths were erected, while analyses of the waters were 

 made, books and pamphlets were written on the subject, and people went to be 

 cured of every kind of complaint : in the majority of cases these Spas are simply 

 of local historic interest.^ 



Manufactories of various salts from Mineral Waters have been carried on at 

 Leamington, Cheltenham, and other places. 



While some springs on the whole manifest great uniformity in 

 their composition, yet they are liable to vary in abundance and 

 strength, and in the quantity of gases given off, such as nitrogen, 

 carbonic acid gas, carburetted and sulphuretted hydrogen. 



Mineral Springs have been classed as follows : — 



^ G. F. Playne, Proc. Cotteswold Club, vi. Si. 



^ P. Geol. Assoc, vii. 432. 



3 G. Maw, G. Mag. 1866, p. 253 ; see also Ibid. 1S67, p. 305. 



* Prestwich, Q. J. xxxi. 41. 



* See The Spas of England (Northern and Midland Spas), by Dr. A. Granville, 

 2 vols. 1 84 1. 



