1822.] 
from their lamillar character, interlaid by 
various other thick rocks of a massive and 
stony character, most of them not at all la- 
minated, and which latter rock have there- 
fore, along with very numerous others com- 
posing the bulk of Wales, been often impro- 
perly denominated slafe-rocks ;_ grey-wacke 
slate rocks, some would now call them, but 
Mr. Farey, though disapproving the use of 
the term slate in this case, still adheres to the 
name given by him in 1811 to rocks of a si- 
milar character in Charnwood Forest, viz. 
coarse slate, The breadth of surface made 
by the slate series is not less than two miles ; 
the bridge over the Ogwen at Ogwen Bank, 
near the great Penrhyn Slate Quarries, at 
five miles SE. by S. of Bangor, stands upon 
or near to the south-eastern limit of this 
series, near where this limit crosses the new 
parliamentary road from London to Holy- 
head ; and a new bridge on this road, over 
the Ogwen, at two miles and a half SE. from 
Bangor, stands on the most north-western 
rock of thisseries. 
The range of this series of strata north- 
ward from the Ogwen, is nearly N.NE.; but 
in the contrary direction this range is near 
SW. by S. owing to a slight curvature of the 
strata, amounting to about 13°, where they 
cross the vale of Ogwen. The dip is very 
rapid or steep, appearing almost upright in 
some places near the south-eastern part of 
this series, but in proceeding thence north- 
westward, there appears a general tendency 
to a decrease of the dip, which continues to 
the coast, near to which the dip does not in 
places exceed J in 1, or 45°, and the direction 
of this dip, seems invariably to the sowth- 
eastward, whereby these strata appear to pass 
in under the Snowdonian mountains. 
This same direction in the dip of the coarse 
slate rocks, seems, with a very few local ex- 
ceptions, to continue from Ogwen Bank, 
along the line of the parliamentary road, past 
Corwen and Llangollen, to where this vast 
coarse slate series passes under the uncon- 
Jormable rocks of the coal series, near to the 
great Pont-y-Cyssylte aqueduct. In like man- 
ner, from near Bangor north-westward, the 
same direction of dip of the coarse slate se- 
ries to the south-eastward continues, perhaps 
with some trifling local exceptions, across 
Anglesea, having on its surface, two lengthen- 
ed hollowsin a NE. and SW. direction nearly : 
one of which hollows or troughs, on the 
coarse slate, nearly coincides with the Menui, 
and the other with the Cefni river, in which 
hollows, unconformable portions of the coal 
series are seen, underlaid by the limestones 
of that important series. The Anti-Smithian 
Subscription Map, published in May, 1820, 
is, as to these points, pronounced by Mr. 
Farey to be exceedingly erroneous, and in 
nowise answering the high expectations which 
were previously raised concerning it, or justi- 
fying the encomiums which some of its rever- 
end partizans are in the lybit, of bestowing 
upop it, The colours of the slate in the 
Report of Chemistry and Experimental Philosophy. 
251 
Carnarvonshire, slate series are very various ; 
usually they are distinguished into blue, pur- 
ple, green and red: the former is in fact a 
grey purple, others are blueish and reddish 
purple, grey light green, and bright or cherry 
red. Nearly all the slate here raised, seems 
very durable; but that from the blue or 
highest rock of the series, is in the greatest 
repute, not merely for its colour, but the 
flatness and thinness of its lamina, which 
yet are not apt to separate spontaneously on 
exposure to the weather. 
M. Bizto of Venice, says, “ in repeating 
the beautiful experiment of Brugnatelli on 
the colouring matter of coffee, I observed 
that when a drop of the infusion or decoction 
of the grain fell upon a piece of cloth, it 
formed a yellow spot surrounded with a beau- 
tiful green border. 1 attributed this green co- 
lour to the oxidation of the oil of coffee. In 
order to fix that colour I boiled a hectogram- 
me of coffee powder and reduced the decoc- 
tion to eight hectogrammes. I added an 
equal quantity of sulphate of copper dissolved 
in water, and used as a precipitate a solution 
of caustic soda. A deposit was formed weigh- 
ing 105 grammes, which, on drying in the air, 
took a green colour; the more it was exposed 
to the air while it remained humid, the brighter 
the colour became. Water, ether, alcohol 
and the alkaline subcarbonates had no effect 
on the colour. Ammonia indicated the pre- 
sence of copper; caustic potash changed it 
to sky blue, and took itself a green colour ; 
caustic soda did not alter it, and received but 
a slight tinge of the green. The deposit, 
which is a true lac, resists acids sufficiently 
well, and, with the exception of the sulphuric 
and oxalic, no others destroy the colour to- 
tally. Acetic acid in dissolving this lac pro- 
duces a solution of a much finer green. 
Mr. Jonx Murray has published some 
curious observations on the temperature of a 
room indicated by two thermometers at di ffer- 
ent altitudes. Two thermometers being 
placed one on the floor, and the other sus- 
pended 6} feet above it, between the 5th and 
24th of November, indicated differences ot 
from 1} to 5°, the greater heat being in that 
6} feet above the floor. He says that 
Breguet’s Thermometre Metallique, in a 
still room without a fire, in the summer 
months, readily communicated the difference 
in temperature between the floor and a chair, 
and between this last and the table. 
Captain Basit Haut, states that oceulta- 
tions of the stars by the moon are easily dis- 
cernible at sea; and that he himself has 
made several observations of this kind. This 
mode of determining the longitude would be 
much preferable to that by the eclipses of 
Jupiter’s satellites, 
Dr. SzrBEcK has communicated to the 
Academy of Sciences at Berlin, in three dif- 
ferent sittings; a discovery on the magnetic 
phenomena inherent in all metals and many 
earths, according to the difference of the de- 
grees of heat. 
BRITISH 
