216 Dr. Marcet on an Aluminous Chalybeate Spring 



" plish argillaceous slate of a fine grain, disposed in thin layers 

 " with a few specks of silvery mica interspersed through the 

 " mass. Black stains, or impressions of vegetables, are seen on the 

 " natural j oints of this rock. Above this, lies a stratum of several 

 " fathoms in thickness, of a bluish calcareous marl, with specks of 

 " mica, which has an earthy and friable texture, and contains im- 

 " bedded nodules or kidneys of sulphuret of iron. Many of these 

 " nodules have undergone a partial decomposition, to which, no 

 " doubt, the existence of the principal ingredients of the spring is to 

 " be ascribed. The upper strata of the cliff are composed of a cal- 

 *' careous free stone, alternating with a coarse shelly limestone, ac- 

 " companied by nodules or layers of chert or flint. 



" As the same arrangement of rocks here observed prevails in 

 *' several other parts of the Isle of Wight, and even along the coast 

 " of Hampshire, it is not improbable that other springs of a similar 

 *' nature might be discovered. May not Alum Bay^ which lies 

 *' to the north of the Needles, have derived its name from a circum- 

 " stance of this kind ? 



" On the road from Shorwell to Chale, the soil consists of a ferru- 

 " ginous sandstone, and chalybeate iridescent waters are to be seen 

 " in several places. To the east of Fresh-water Bay, not far from 

 " the place where the cliffs of chalk begin to make their appear- 

 ** ance, there is a rivulet, the taste of which strongly indicates the 

 " presence of iron. At Blackgang Chine, a little to the N.W. of 

 " the aluminous chalybeate, is another ferruginous stream running 



partial combustion. When submitted to chemical analysis, it yields a quantity of iron, 

 but no lime, nor aluminc, nor any other earthy matter soluble in an acid. Close to the 

 spring, this sand contains some traces of sulphuric acid, but not at a distance from it : 

 it is evident therefore that the sand-rock is not the medium through which the spring is 

 impregnated. 



