86 



the weir which carries off its surplus waters a deposit of Tufa is 

 now accumulating. 



It is possible that other considerable deposits of tufa besides 

 those at Chalford and at Dursley have taken place in our district, 

 and are covered up by landslips or by vegetation, and it is 

 certain that there are many springs capable of producing such 

 dej)Osits if only the requisite conditions existed. Considering 

 the value of this material for building purposes, a value so well 

 understood by the builders of ancient and modern Rome, as 

 proved by the great use they made of recent deposits of 

 " Travertine," it is a question whether Calc-tufa might not be 

 profitably produced by artificial appliances. To a proprietor 

 of an estate possessing abundant springs charged with Carbonate 

 of Lime, an artificial disjDOsition of their waters with a judicious 

 planting of Hypnum cominutatum might be as profitable an 

 investment for futurity as the planting of oak trees. 



There are other forms of calcareous deposit to be mentioned 

 beside that of Calc-tufa — namely, such as take place by the 

 action of percolating water in the strata of our hills. Much of 

 the Carbonate of Lime resulting from this action is immediately 

 re-deposited as Calc-sinter in the rocky beds of the Cotteswolds, 

 coating the sides of crevices, and forming stalactites ; and in 

 the strata, which are formed of small rubbly stones, the effect of 

 an infiltration of this Carbonate of Lime is often to convert such 

 beds into a mass of rude conglomerate. In many quarries the 

 strata are found thus " callised " as the workmen term it, and 

 whilst this has added to the labour, it has also added to the 

 safety with which these quarries can be worked. In the 

 Cotteswolds the stalagraitic deposits of Carbonate of Lime are of 

 little economic value, but specimens are occasionally met with 

 which illustrate the mode of formation of many valuable marbles, 

 such as the beautiful "Onyx marbles" of Algeria. A specimen 

 of Calc-sinter from Woodchester Park has such a compact sub- 

 crystalHne texture and concretionary structure, the successive 

 layers of deposit varying in colour owing to their containing 

 extraneous matters in varying amounts. 



Calc-sj>ar is frequently met with in the various strata of our 



