SCO Mr. Saxton oh his Mag7ieio-electrical Machitie ,- 



The BEDS of SAND immediately above these flints are of 

 different kinds. 



At New Charlton it is a fine white sharp sand, and is used 

 'in the foundries about London. The sand at Old Charlton 

 is almost as good, but it is chiefly used for sanding floors. 

 At Erith, Purfleet, and Grays it is only fit for ballast. But in 

 the trenches dug by Mr. Rosier, and at Elmstead, it is quite 

 different. On taking samples of this sand to London and 

 washing it, and examining it when dry, I found it to be sand 

 exactly the same as that which is well known near London as 

 brickmakers' sand, which is exceeding soft when felt between 

 the fingers, and is used for sprinkling the brickmakers' moulds 

 to prevent the adhesion of the clay. It is obtained for that 

 purpose from above the mud opposite to Woolwich, and off 

 Crayford Point, and is, no doubt, washed down by the rain 

 and brought into the Thames by the rivers Cray and Darent 

 from the districts througli which they run. 



In respect of the chalk immediately below these beds of 

 flint, in most of the localities examined the surface is perfectly 

 level, even, and unbroken ; and it is not furrowed and indented 

 as some observers have represented the upper surface of chalk 

 always to be. 



That opinion must have been formed from the circumstance 

 of the chalk, in almost all places where it is near the surface 

 of the ground, having suffered much diluvial action ; and from 

 chalk-pits generally being opened, from a motive of saving ex- 

 pense, on the sides of hills, v^here there is little top surface to 

 be carried off. In the pit at Elmstead it is, however, different 

 from the other localities. There the chalk is cut into ridges, 

 the hollows of which are filled with these flints and clays co- 

 loured with iron : which is a proof that in one instance at 

 least the chalk may have suffered diluvial action before the 

 formation of these flints and of the beds of sand over them; 

 but being only one locality out of twenty-one, it shows that 

 the general rule is otherwise. 



LXX. Mr. J. Saxton on his Magneto-electrical Machine ,- 

 with Remarks on Mr. E. M. Clarke's Paper in the preceding 

 Number. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 T REGRET that I am called upon to notice a very disin- 

 genuous article in the Number of the Philosophical Maga- 

 zine for October. A reader unacquainted with the progress 



