IIARDWICKE'S SCIENCE-GOSSIP. 



97 



ON LAND SUBSIDENCES. 



By Dr. CRESPI. 



VERY one has 

 heard of the land 

 subsidences in 

 the salt districts 

 of Cheshire, 

 where lakes form 

 and houses 

 threaten to fall in 

 a manner that 

 rather shakes the 

 nerves of the 

 timid. But every 

 one is not aware 

 that Droitvvich, 

 in Worcester- 

 shire, is more 

 slowly but not 

 the less surely 

 sinking into the 

 ground, or rather 

 I ought to say, 

 that parallel to certain lines the land is sinking, and in 

 this way much destruction of property is taking place. 

 Wherever for many years large quantities of minerals 

 are removed from beneath the surface of the ground, 

 there must in time be a settling of the superficial 

 strata, and this settling is slower when the quantities 

 of material removed are small and from a great depth, 

 while, when the amount removed is large and near 

 the surface, the subsidence is far more rapid and 

 destructive. Near Dudley, the educated eye sees 

 on every side signs of land subsidence, and in many 

 other parts of the Black Country houses are shored 

 up, walls are cracked, and a general though unequal 

 sinking is obviously taking place. There is, however, 

 nothing unusual in the settling at Droitwich, nor is 

 the sinking on a very alarming scale, and, so far, it 

 has not been marked by terrible catastrophes, only 

 one house having totally collapsed and in that in- 

 stance no lives were lost. 



Droitwich is not a prepossessing place : it is not 



tastefully built, and is somewhat dingy ; the houses 



are mostly shabby, and the shops small, and there 



No. 281. — May ii 



is little to distinguish it from a host of other fourth- 

 rate manufacturing towns which chiefly strike the 

 visitor by their dulness, smoke, and dirt. The country 

 round the town is, however, extremely pretty and 

 very fertile, and there is no difficulty in getting away 

 for a few hours to many of the prettiest and most 

 delightful spots in England. But the fame of 

 Droitwich, such as it is, is connected with its 

 brine, and were it not for inexhaustible supplies of 

 the purest and strongest brine in the world — the 

 residents say the purest and the best found any- 

 where — no one twenty miles off would have heard of 

 the grimy little town, through which the Midland 

 expresses tear without stopping on their way from 

 Cheltenham to Birmingham. 



To the Romans the town was well known, or rather 

 it is to the Romans that it owes its foundation : that 

 great, wise, and enlightened people discovered the 

 properties of its brine springs, and with characteristic 

 energy set to work to extract salt from the water that 

 at that time welled up to the surface in inexhaustible 

 streams. As the brine is nearly saturated and con- 

 tains two-fifths of its weight of salt, and only requires 

 to be evaporated to yield a pure residuum of salt, 

 the process of salt extraction (for it is not fair to call 

 it salt manufacture) is easy and simple. 



At present over 115,000 tons of salt are extracted 

 every year, and allowing that four times as much 

 brine is pumped up in the course of the year, half 

 a million tons are removed from a depth of 200 

 feet or thereabouts. Whether the brine comes from 

 deep reservoirs or from salt beds traversed by sub- 

 terranean streams — the explanation locally hazarded — 

 is immaterial : the fact remains, that the removal of 

 such vast quantities must in time lead to decided 

 sinking of the surface ; and as this sinking or'rather 

 these areas of subsidence are of irregular size and do 

 not include the whole town, although they in some 

 directions extend far beyond its boundaries, the visitor 

 is prepared to learn that, in twenty years, the sinking 

 has reached 19 feet. I do not vouch for the accuracy 

 of this calculation. 



On leaving the station and making our way into 



F 



