70 PHILOSOPHICAL TRANSACTIONS. [anNO 1757. 



incrustation, which had been made by the water since the last cleaning ; and if 

 neglected would (as it has sometimes actually done) choak the passages, and 

 oblige the spring to find vent in some other place. The incrustations formed 

 by these waters are of different kinds : that which is made in the troughs and 

 pipes, through which the water is conveyed after it comes above ground, is of a 

 light sandy nature, of a loose contexture, and a bright yellow. It is used by the 

 inhabitants as a gentle corrosive for eating off proud flesh. There is another of a 

 darker colour, and a much harder nature, found at the very mouth of the spring, 

 where it bursts out of the rock. There are other sorts taken out of the sub- 

 terraneous cavities of the spring at the time it was cleaned. They seem to be an 

 alabastrine spar, and are beautifully marked with straight veins of different co- 

 lours, which may be supposed to have received their tinge from the different 

 colour of the spring water at the time whan this sediment, or rather scum, was 

 formed on it. They find pieces of this kind most beautifully variegated ; and 

 some of them large enough, by fineering, to make tables : these polish very well, 

 and are not much inferior to jasper in appearance. It is a part of the manufacture 

 of the place, to work this part of stone into snuff-boxes, cane-heads, and sleeve- 

 buttons. 



There is another sort of incrustation, different from all these, which was found 

 some years before in digging for the foundations of the new parish church, 

 which is about 3(X) yards distant from the Prudel spring. They found there 

 the same kind of water ; but it did not rise with so great force as in the other 

 spring : and they discovered in the cavities large masses of a stony concretion, 

 which were a sort of pisolithi, most of them in a globular, but some in an oval 

 form, from the smallest size to that of a nutmeg; the former sort lying in masses, 

 the latter generally single and detached : they are perfectly white, hard, and 

 smooth, and appear, to consist of a great number of lamellae formed round a 

 small nucleus. This sort of incrustation has been found in no other place ; but 

 there are some of a browner sort, and more irregular shapes, which are taken 

 out of the Prudel. 



The medicinal virtues of these waters have been treated of by German au- 

 thors. They are esteemed to be particularly efficacious in removing obstruc- 

 tions, and in cases of the stone and gravel ; of which the treatise lately produced 

 to the Society contains many remarkable proofs. They are much frequented in these 

 and other cases ; so that they have generally 200 persons in a season drinking 

 the watrrs. The season begins in May, and ends in August. They drink them 

 in the following method. They begin with a purge ; and assist its operation 

 with 10 or 12 chocolate-cups of the water, taken within 5 minutes of each 

 other. The day following they take the waters in the same quantity, and at the 

 same intervals, keeping themselves all the time in a warm room ; which, with 



