Earths. MINERALOGY. Earths. 457 
two portions taken From different parts of the fame rock. 
See the fubjedt purfued more at large under the article 
Basaltes, vol. ii. There are lix fpecies. 
1. Bafaltes fchiftofus, or flaty bafalt : black of a flaty 
texture. Found in bafaltine mountains on the Rhine, 
and in the neighbourhood of Gottingen ; commonly 
abounding in particles of olivin. 
2. Bafaltes columnaris, or columnar bafalt: of a dull 
colour, compadt, hardifh, tenacious, ipontaneoufiy break¬ 
ing into prifmatic granular fragments. Found in various 
parts of the Britilh Blands, particularly in Staffa in Scot¬ 
land, and the Giant’s Caufeway in Ireland, in the South- 
Sea Iflands, Sicily, Italy, France, and many other parts 
of Europe, generally forming the bafe of mountains ; of 
a columnar lhape, ftraight or curved, perpendicular or 
inclined, rarely parallel ; the diameter of the columns 
from three inches to three feet, fometimes with tranlverfe 
hemifpherical joints, in which the convexity of one is in¬ 
fected into the concavity of the other; their form is pen¬ 
tangular, liexangular, or octangular, rarely triangular or 
quadrangular. Colour bluifli or greenifh-black, or dark 
greyilli blue, varioufly interfedted with veins of white cal¬ 
careous Ipar, and often the impreffions of various foible 
bodies and flmibs. They are rather hard and difficult to 
break, feel harlh, and found under the hammer. Texture 
earthy ; fradture uneven ; break afliy-grey. Specific gra¬ 
vity, from 2’864*to 3 - ooo. A fpecimen from Staffa con¬ 
tained filex 44, alumine 16, oxyd of iron 16, lime 9, wa¬ 
ter 5, foda 4, muriatic acid 1. We have given the pro¬ 
portions of other fpecimens under the article Basaltes, 
before quoted. See alfo Giant’s Causeway, vol. viii. 
p. 548. to which we lhall here add a few words by way of 
comparifon (as a comparifon has been made) between this 
moll llupendous natural phenomenon of Ireland and the 
colonnades of Staffa in Scotland. This we lhall copy 
from Dr. Richardfon’s Appendix to Mr. Dubourdieu’s 
Statiftical Survey of Antrim : “ I do not with,” fays Dr. R. 
“ to derogate from the beauty, nor to depreciate the gran¬ 
deur, of the Staffa colonnades ; but, as Mr. Pennant in- 
ftitutes the comparifon, I mult tell him that, while the 
longelt pillar at Staffa is 55 feet, ours at Fair-head are 350. 
The continuous colonnade at Fair-head is longer than the 
whole ifland of Staffa ; and the colonnade at Bengore 
three times as long, and one of its two parallel ranges of 
pillars equal to the folitary range in Staffa. Though I 
never faw Staffa, I may fairly pronounce our facades to 
be far more llupendous ; for the higheft point in the illand 
of Staffa is but 126 feet above the level of the lea, while 
Plelkin, fcarcely higher than the reft of the fagade, is 370, 
and the uniform columnar range of Fair-head 550.” 
3. Bafaltes pyramidalis, or pyramidal bafalt: of a dull 
colour, compadt, l'pontarteouily falling into pyramidal 
fragments. Found in the mountains of Bohemia, near 
Auffig, in elongated three-fided fragments; and in Hun¬ 
gary, near Schemnitz and Cremnitz, in four-lided frag¬ 
ments. 
4. Bafaltes tunicatus, or clofe bafalt: compact, fpon- 
taneoufly falling into cruftofe fragments ; the crufts 
fpheric.b and concentric. Found with the B. columnaris ; 
is a little fofter, with a paler tinge, and crumbles more 
eafily. 
5. Bafaltes wacca, or wacken : foft, fragile, compadt, a 
little glolfy when rubbed, not falling fpontaneouffy into 
fragments. Found in the mountains of Bohemia and 
Saxony ; fometimes in entire ftrata, fometimes in thin 
layers under or between bafalt. Colour cinereous, or 
greenifli, or blackilh, or yellowifh ; often contains veins 
of metallic ores; luftre none, fradture even, texture 
earthy, opake, foft, eafily broken, and feels llightly greafy. 
It withers by expofure to the atmofphere, and then be¬ 
comes more grey; frequently contains black mica, but 
never olivin. 
6. Bafaltes trapezum, or trapp : hardifh, compadt, im¬ 
bibing water, growing reddiih in the air and mouldering 
¥01. XV. Ho. 1057. 
into lamellar pieces, crackling and breaking with explo- 
fion in the fire. 
Wallerius calls this fpecies Corneas trapezius; partly 
from that horny roughnefs which belongs to it in com¬ 
mon with feveral other minerals called hornftones, and 
partly from its natural difpofition to feparate into trape¬ 
zoidal or irregularly four-fided figures fomcwhat refem- 
bling fteps or ftairs ; the Swedifh word trapp fignifying a 
ltep or ftair. Wallerius obferves, that he fliould have been 
inclined to call it Corneus J’calaris, but for the coinci¬ 
dence between the terms trapp and trapezius as applicable 
to the form which its fragments are difpofed to affume. 
It is found in the mountains of Britain, Scandinavia, 
Swilferland, and Germany, forming vaftmaffes, and often 
broken into three, four, or five, tided prifms. Colour 
greyifli, bluifh, or purplifh-black, black, blackfill, or red- 
difh-brown ; and frequently containing bafaltine, quartz, 
cryftallized carbonat of lime, felfpar, and olivin : hence 
it is frequently porous, cellular, or cavernous, from the 
decompofition or falling out of thefe Hones ; fradture 
earthy or fine fplintery, often uneven. It effervefces a 
little with acids, and may be melted into blackiih-green 
glafs. There are three varieties. 
1. Toarljlone. Of a dark brownifh-grey colour, abound¬ 
ing with cavities filled with cryftallized carbonat of lime, 
which from the deltrudlion or decompofition of the cryf- 
tals are often empty. Contains filex 63, alumine 14, mild 
carbonat of lime 7, oxyd of iron 16. 
2. Ferrilite. This term has been applied by Mr. Kirwan. 
to the variety commonly known by rhe name of Rowley 
rag; which is either a corruption of Rowley-regis, near 
Dudley, in Staft'ordlhire, where it is found ; or is given to 
it in common with many other fubftances which by the 
common people are called rag-ltones. The following 
account of it is taken from Mr. Gregory Watt’s paper in 
the Philofophical Tranfadtions for 1804. He fays it is 
met with in the fouth-well part of Staffordfhire ; that it is 
tiled for polilhing in fome of the manufadtures of Birming¬ 
ham, and has been particularly recommended for grind¬ 
ing the fpecula of reflecting telefcopes. It is of a con¬ 
futed cryftallized texture ; its fradture, in fmall pieces, is 
uneven ; in the large, conchoidal. Its liardnefs is fiupe- 
rior to common glals, but inferior to felfpar ; its tenacity 
is conliderable; its adtion on the magnetic needle is ftrong, 
but without iigns of polarity ; its fpecific gravity is 2 - 8o8. 
The general colour of Rowley rag is a very dark grey, 
approaching to black; it refledts light from a variety of 
brilliant points, fome of which leem to be felfpar, the 
others hornblende. According to the analyfis of Dr. Wi¬ 
thering, 100 parts contain 47"5 filex, 32-5 argillaceous 
earth, and 20 of the oxyd of iron. The magnetic pro¬ 
perty of thefe rocks was firlt obferved by Dr. Plott, who 
lays they turned the needle 6° from its proper diredtion. 
The fame power of affedting the magnet has fince been 
difcovered in feveral bafaltic mountains, particularly in 
the Giant’s Caufeway in Ireland. This ftone is limilar to 
the bafalt of the Clee-hills, in Shropihire, and the bafaltic 
ftones in various parts of Great Britain, In its characters 
and chemical compofition it nearly relembles fome of the 
compadt lavas from Etna and Teneriffe. It. is eafily fu- 
fible into an opake black glafs, which, however, tranfmits 
light through very minute fragments : the texture of this 
glafs is completely vitreous, with a few air-bubbles ; its 
fradture is conctypidal and undulated ; in hardnefs fupe- 
rior to felfpar, but inferior to quartz : this glafs pofleffes 
fcarcely any adtion on the magnetic needle. The fpe¬ 
cific gravity is 2749. 
Mr. Watt made numerous experiments upon this fub- 
ftance, correfponding with thole which had been previ- 
oully made by fir James Hall on the different effects pro¬ 
duced by the rapid or flow cooling of vitrified whin or 
bafalt; diredting his attention principally to the cryltal- 
lization that took place in the interior. By withdrawing 
the heat very gradually from the vetrified raafs, he found 
6 fk that 
