Star.
London, England, 1811-05-13 00:00:00

- Apra, INS7'ITUTION. •

WO. DAVY'S SECOND LECTURE ON GZOLQGY.
In this Lecture Mr. DA tit described two species of
cliaracters to be attended to in the study of Geology
those which itistil.tied specimens of rocks pre-
sent, such as physical qualities, constithent parts, &c.
the other, the aspect of rocks considered as great
masses, or their general features, such as' outline from.
colour, strAtifieAtion, &c. . •

In the primary order of rock' he pointed one and
described six clasies. These, he observed, included
all tucks strictly belonging to this order. He exclu-
ded argillaceous and si,icious schist, because water-
worn stones or shells occur hi them, and the topaz
Rock of Werner, as having more the appearance of
pait of a vein. Granite, micaceous schist, scinite, ser-
pentine porphyry, and nimble are primary rocks.—
All these arrangements ave,eonstituted by a few
crystalline substances, which are principally quartz,
feldspar, MICA, hornblend, tale,, and calcareous spar,
Thus granite is an aggregate of crystal, of quartz,
mica. ;and feldspar, and scinite of spiarti, feldspar,
acid honiblend— micaceous tchist,..t quartz, and mi-
ca—serpentine, of skitter spar, talk and feldspar, con-
taining veins of steatite.
The mechanical constituents of rocks are few; but
their chemical elements ale-still less numerous. When
subjiictedto analytical processes, they afford :ilex, alu-
snilia magnesia, lime, fixed alkali, and oxide of iron.
These substances variously combined, give rise to the
great variety of the forms and appearances of their
chrystals—and Mr. Davy's late discoveries prove,
that the earths and alkaties have metallic bases, and
that they are compounds of these bases and oxygene.
In the arrangetnent of the primary rocks a certain
order and relationship is generally to be observed—
granite is the highest and deepest rock, it forms the
summit of the loftiest mountains, and seems to be
the foundation of our continents, and islands, and is
usually covered by geognies (itself a species of gra-
ttite),-micaceous schist, or sienite. Serpentine and
marble occupy the middle stations of mountain chains,
and are oftener found upon micaceous schist than upon
granites.
Porphyry is mostly associated with granite, and is
frequently immediately incumbent upon it. The pri-
maryrocks constitute the principal solid part of the
surface of otir globe, and form the loftiest mountains,
• and their geographical position is admirably adapted
to preserve the order and economy of the system.—
The heights of mountains in general diminish from
the equator towards the poles. In hot. climates the
effects-of mountains are tolower the temperature of
• the subjacent countries, and thus most of the tropical
regions are rendered habitable. Where, mountains
do net occur, as in Africa. there are sandy desares--
mountains too are the sources of streams and rivers,
they attract clouds, condense vapour into water; and
pour it into the rallies and plains—they modify the
course of the winds, and shelter the lowlands.
In all systems for explaining the formation of pri-
.
mary rocks, a fluid state either from igneous, or
itqueolis fusion is assumed, but it is not yet explained,
Mr. Davy remarked, why different chrystals should
ocoarate in the same mass. The chrystals produced
either from solutions or by 5105 cooling in artificial
Or natural operations are uniform, and nut of different
Species, like these of the primary rocks, so that the
• solution of this grand problem, if it be capable of so:
lution, must be gained from the improvement of che-
mical science. Nature may produce effects by powers
which have not, as yet been discovered, and her re-
sources should never be estimated by our operations.
Mr. Davy, in the course of this lecture, mentioned
the applications of the cubstancei derived from the
different primary rocks, to the uses of common life,
and particularly pointed mit their applications to the
purposes. of Architectfire. Granites, porphyries, and
swishes, are the most durable stones; micaceous schist
anti serpentine, are much more liable to decay. The
most perfect f the worts of the • Egyptians, those
least injured by time, are of granite. This stone or
porphyry should be used for all great public monu-
ments. Mr. Davy, in touching on this subject, said,
be could not avoid introducing t few observations on
the little attention paid to such public memorials in
this great country. Yet, said he, Our materials are
Copious ; our harvests of glory arenas' a rich, nay even
more abundant than those of the gat elder nations.
Why should Cie spirit be wanting' by which they are
'to be gathered in and made permanent ? We have
bad philosophers who are the glory of the whole hu-
man race. IA eroes and Statesmen, rivals of the illus-
• trious of Athens and of Rome. Yet this metropolis
offers no great durable tribute of respect to our science,
, and our naval and military glory ; and in a thousand
years, though there may ba a new and mare magni-
ficent city on the banks of ;he Thames, yet there will
scarcely be a wall of what we new behold standing.
'Nothing to speak to posterity of what we are in these
memorable times. In our Philosophy, the Guides ;
in our Literature, the Instructor;; and, in our Poll-
tics, the Saviours of Europe;
Nor would such works be devUid of immediate uti-
' litr and beneficial efface.
A few columns raised to the illustrious dead ; a
few niticnial laboratories, or museums, devoted to the
memory of great men, and to the use of students,
would rise as land-rnarks of fame, would continually
excite to excellence. No motive for exertion is so
strong as that founded upon the sympathy of the good
.ad wise ; n.a reward so sweet as that of being held
up to public admiration, as a benefactor of the spe-
cies ; nu g;ory so pure, so calculated to awaken great
.minds, as that of immortality!
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- Ma. DAV I.EC CURE.
In this Lecture Mr. Davy described the secondary
vntks, or the rocks containing fragments of the pri-
• wary substances, and the remains of organized beings.
He divided these rocks into three families, and illus-
trated their nature and their arrangements by sped-
piens . audby paintings. The first Lundy, he stated,
COntains nearly the. same elements ps the primary
rocky It' comprehends the secondary granites, mica-1
eeous schists, sienitss, porPhyriesOcc. They differ from
the primary rocks of the same name, by the occur.
vence at fragnients, principally of water worn quartz,
and :hey du not appear in considerable masses, bat
in beds .or veins ; these rocks. are-much more abun-
dant in metallic ores -Than. ire primary rocks ; They
awe not so proper for architectural purposes, being
me decomposition, but. when deco ngesed they

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