ECONOMIC GEOLOGY. 251 



CHAPTER XVI. 

 ECONOMIC GEOLOGY. 



The Isle of Wight has no mining industries and few quarries 

 or pits, except those for freestone, chalk, sand, and brick-earth. 

 Hydraulic cement is made at the West Medina Cement Works from 

 chalk and Oligocene clay, and at Brading Cement Works from 

 the Bembridge Limestone and Marl. The Wealden Shales are 

 used for brickmaking at Sandovvn, as well as deposits of brick- 

 earth, associated with gravel, near Borihwood. At Shanklin a 

 bed of clay in the Lower Greensand is dug by the side of the 

 railway for the same purpose (p. 46). The Gault is worked at 

 Bierley, Rookley, and by the side of the railway between Wroxall 

 and Shanklin (p. 64). An extensive deposit of brick-earth near 

 Brixton has received little attention from the remoteness of that 

 district ; the bricks for the viaduct of the Military Road over 

 Grange Chine were manufactured from this deposit (p. 224). 

 Brick pits are opened in various parts of the superficial and 

 Oligocene Beds, but curiously enough the bed that would probably 

 make the best brick-earth — the free-cutting decalcified loam so 

 often met with in trial borings low down in the Hamstead Series — 

 has not been used. Tiles and coarse pottery can be manufactured 

 out of the Reading Beds. The white pipe-clay in the Bagshot 

 Beds is no longer worked, the bed being thin and so nearly 

 vertical that it can only be reached by mining. 



The Bembridge Limestone was formerly much used as a 

 building stone, but the principal quarries are now worked out, and 

 brick ig generally preferred. The limestone stands the weather 

 very well, though the large cavities left by the fossils are often 

 objectionable and much of the stone is too soft for use. The sea- 

 walls round the northern portion of the Island are generally built 

 of Bembridge Limestone. A better building stone is obtained 

 from the four-foot freestone of the Upper Greensand, described on 

 pp. 64-72. This bed has been worked from time to time throuo-h 

 a larger part of its outcrop in the central and southern parts of the 

 Island, but the principal quarries, now in use, he around Shanklin, 

 Bonchurch, and Ventnor. Road metal is obtained from the 

 Angular Flint Gravel on St. Boniface Down (p. 210), from the 

 Plateau Gravel on St. George's Down (p. 212), and from the Valley 

 Gravel at Horringford (p. 221). There are many smaller pits 

 scattered about, which have been referred to in the description of 

 these gravels in chapter xiii. 



