404 Application of Mineralogical and Chemical Science [June 1, 
at. Charnwood forest, in Leicestershire. 
The granite is chiefly used for paving in 
the neighbourhood ; it is small-grained, 
or what some mineralogists would call, 
-secondary granite; and others sunite as it 
contains small crystals of hornblende. 
Its specific gravity I found 2.77. It is ex- 
tremely hard, and is worked by blasting. 
If it can be raised in blocks of sufficient 
magnitude, it might be employed with 
great advantage in constructing the foun- 
dation of the new bridges; as-it is only 
one hundred miles distant from London, 
from whence there is direct carriage by 
water, It is, I believe, the most. durable 
stone that can be found in any great 
quantity at the same distance trom the 
anctropolis. At the same place is pro- 
cured another stone, resting upon the 
granite; it is a species of greenstone, and 
hornblende porphyry, containing small 
crystals of felspar, in a basis chiefly of 
hornblende. The workmen informed me, 
it is broken with more difficulty than 
granite; it is not so hard, but is very in- 
frangible. Its specific gravity I found 
£.88. It contains some oxyd of iron, 
like other stones of this species, which 
may perhaps render it improper to be 
used, where it can be acted upon by 
water; but it has every appearance of 
being a very durable stone, and might 
deserve the attention of builders, where 
great strength of materials is required, 
Iu silicious sand-stones, the coarseness 
or fineness of the grains is of less im- 
portance than the substance in which 
they are imbedded. Those which have a 
basis of ferruginous clay, are soft and 
perishable; but when the basis itself is 
of a silicious kind, the stones are almost 
equally durable with granite. The upper 
strata of many of the highest hills in 
Yorkshire and Derbyshire, are of this 
kind, which Mr. Whitehurst calls a mille 
stone grit. It is ofa finer-grained stone, 
of the same kind tbat Kirkstall Abbey, 
near Leeds, is built. Though the Abbey 
is a ruin, the stones which remain are 
little decayed. After the lapse of six 
hundred years, they preserve their an- 
gular sharpness, and the impression of 
the chissel, «5 fresh as if they had been 
recently worked. There is a quarry of 
this stone in the neighbourhood; and I 
have observed some of the stones in the 
London docks, are of a similar kind. 
Some silicious sand-stones appear to be 
of alluvial formation, and have their parts 
ao imperfectly cemented, that they are 
unfit for the purposes of architecture ; of 
this kind are the rocks on which the tewn- 
, 
of Nottingham is built ; and the red-sand 
rock of Chesbire, The former may be 
considered more properly as indurated 
gravel, intermixed with rounded. quartz 
pebbles; but, though it is too loose to be 
applied to purposes of architecture, it 
may be excavated to a considerable ex 
tent, without the necessity of supporting 
the sides and roof. ‘The granite of 
Charnwood forest, and the loose sand- 
rock of Nottingham, are not more than 
twenty miles distant, bat they may be 
considered as forming the two extre- 
mities of the scale of aggregate silicious 
stones, from the very hardest to the 
softest kind. Argill, or clay, is never 
found pure in any kind of building-stone. 
It is soft, smooth, and unctuous to the 
touch, and will absorb more then 2% 
times its own weight of water; and, as 
Mr. Kirwan has observed, it commu- 
vicates, in some degree, these properties 
to stones, if it is combined ina proportion 
of from 20 to 30 per cent. In a greater 
proportion it destroys the qualities of 
silicious stones, Many argillaceous stones 
contain a considerable quantity of iron, 
not perfectly oxydated. When exposed to 
the atmosphere, they speedily decay. It 
is in stones of the argillaceous kind, that 
the greatest caution and mineralogical 
knowledge are required, in the selection 
for purposes of durable architecture. I 
have seen a hillock at the mouth of a 
lead-mine, supporting a luxuriant vee 
getation, which a respectable miner in- 
formed me he had twenty years before 
blasted from a compact. bed of toad- 
stone, or basalt, that resisted the pick- 
axe, and no soil had been since thrown 
upon it. An instance of this kind was 
the occasion of an action at the last York 
assizes, between the proprietors of the 
Barnsley canal; and the engineer, On 
the part of the proprietors it was con- 
tended, that the hill through which he 
had to cut a tunnel, was a soft marble, 
On the part of Mr. Pinkerton it was 
stated, that, though the part exposed was 
now soft, it was, when first opened, a 
vers hard and compact rock, extremely 
expensive and difficult to work; and the 
truth of this statement he offered to 
prove, ty perforating any part of the 
hill where the stone had not before been 
laid bare to the action of the atmosphere, 
The argillaceous sand-stone which ac= 
companies or lies over coal, is used for 
buildings in coal countries, as in some 
parts of the West Riding of Yorkshire; 
but it is not suited for public. buildings, 
er works intended te be durable, Stones 
of 
