an the Counties of New-Haven and Litchfield. 217 
excavation, exposes to view a ledge of gneiss in the upper 
part of the mine; it was inaccessible, but from its appear- 
ance and from the fragments which had fallen below, no 
doubt could be entertained that it wae gneiss, especially as 
this rock constitutes all the neighboring couniry. 
The clay which forms the immediate enveloping matter 
of the ore is very interesting. It presents a great variety 
of colours ; of blue, green, red, yellow, &c.—which, with- 
out doubt, arise from the oxid of iron and other metallic ox- 
ids ; good colours for painting might be selected from them. 
Some parts of the clay appear very saponaceous, and the 
workmen assured me that a true fuller’s earth, answering all 
the purposes of that useful mineral, had been obtained 
here. 
A fuller’s earth is a clay usually soapy in its foel—very 
absorbent of grease and oily matters ; fine in its texture, so 
as to present no parts that shall be large and harsh enough 
to injure cloth or wool, mechanically, by rubbing ; it should 
fall to powder easily in water, so as to diffuse itself through 
that fluid, and easily mix with it and with the stuffs to which 
it 1s applied. The fuller’s earth of Hampshire, England, so 
much celebrated, is of a greenish yellow, tolerably firm, 
crumbles easily in water, receives a polish from the finger 
nail,and ts very powerfully detergent. This is, after all, the 
important criterion by which to distinguish fuller’s earth ; 
ifit removes grease with avidity, crumbles easily in wa- 
ter so as to diffuse itself readily,and yet is not so coarse as 
to wear the fibre, it is a fuller’s earth. The subject isof some 
practical importance to this country on account of its wool- 
fen manufactures, which, although checked for the present, 
must eventually rise and prevail. While they are of smal! 
extent it may be better to use soap, but in very large es- 
tablishments, fuller’s earth from its cheapness (provided it 
can be abundantly obtained) is very desirable. 
With respect to the existence of fuller’s earth in the clay 
of the Kent iron bed it appears very probable, and some of 
the specimens appear very like the Hampshire earth, but 
experiments alone can decide. 
This vast bed of clay, (for it occupies more or less tthe 
whole depth of the pit) is without any reasonable doubt, in- 
terposed between ledges of gneiss, which evidently form its 
roof, and appear to form its pavement. 
