338 PHILOSOPHICAL TRANSACTIONS. [anNO 1747. 



it may not be unacceptable to have an account of the pits of it, and whatever 

 else relates to it, taken on the spot. 



This earth itself is a coarse harsh loam, composed of a very large shining sand, 

 of extreme hardness, and a fine soft tenacious clay : its value is its remarkable 

 quality of standing the force of the most violent fires without running to a glass; 

 which makes it extremely useful to all who have occasion for such fires, and is 

 the reason of its being sent not only into all parts of England, but to Holland, 

 Germany, and many other parts of the world. It is used for making the bricks 

 employed in building the wind-furnaces for melting iron, for coating over the 

 insides of assay furnaces, used by the workers on metals, and on many occasions 

 of like kind at the glass-houses, both in England and other nations. 



The place where it is dug is Hedgerley, a small village about 22 miles from 

 London, surrounded with hills, under one of which this loam lies. The pits are 

 about a quarter of a mile south-west from the town, and 5 miles north of Wind- 

 sor : they extend over 4 acres of ground, situated on the descent of a hill ; and 

 were intended to have been carried over much more ground by the person who 

 now works them ; but on trials the loam is found not to extend as was imagined. 



They dig, before they come at this, a very good common brick-clay, a tile- 

 clay, and a potter's earth, a kind of clay of a firmer texture, and deeper colour, 

 than either of those ; but the strata of these are seldom pure or regular, and 

 at the boundaries of the stratum of loam a pure hard sand, evidently the same 

 with that in the composition of the loam, but left loose, from there not having 

 been clay in the way to bring it into the condition of the perfect mass. They 

 have already worked the stratum so far as to find it bounded east and west by 

 beds of this sand, and northward by chalk, and are therefore afraid it will be 

 soon exhausted ; at least, whatever they get hereafter must be procured with 

 more labour and expence, as they have no where to search for it but higher up 

 in the hill ; from whence it must be fetched at greater depths, and much more 

 expence; and this increasing difficulty of procuring it has been the reason of its 

 rising in its price to that it is now sold at, which is 5 shillings a bushel in Lon- 

 don ; but which is not to be wondered at, since on the spot the quantity that 

 makes a thousand bricks, which used to cost Is. 8d. now costs 10s. the 

 digging, and will every year cost more and more, unless a new stratum of it 

 should be discovered somewhere thereabouts, which their many unsuccessful 

 trials make them at present despair of. 



It is to be observed, that this valuable earth forms but a single stratum, and 

 that does not rise and dip with the elevation and descent of the hill, as the strata 

 'of the earth, stone, &c. in hills usually do, but seems to be even and flat at its 

 bottom ; for the higher up the hill they open their pits, the deeper in propor- 

 tion they find the stratum of loam lie. 



