The Liverpool Standard and General Commercial Advertiser.
Liverpool, Merseyside, England, 1838-03-30 00:00:00

LIVERPOOL MECHANICS' INSTITUTION.

• • LECTURES ON GEOLOGY.
On Saturday evening Dr. Sointer.delivered his third lectOre.
If we pay the smallest attention to the different stratas of
rock which we meet with on the surface of the globe,. we shall
find that they may be divided into two exceedingly well classi-
fied classes, which- have been produced•-in totally different
manners, and have occasioned totally different phenomena. First
of all we perceive important series-of' rocks totally destitute of
organic remains placed without any apparent order amongst
the other m•ks, often giving out prolougations, or dykes, or. over-
flowing strata, and of• a highly crystalline structure. They ex-
hibit no traces of stratification, and thus furnish-decisive proofs
that they were not Pirmed• by water, hnt are of chemical origin,
and produced by.volcanic action.. A second. division of rocks
occurs in several beds or strata one above the other. These
beds are generally parrallel to each other. and instead of being
of a crystalline nature have been formed mechanically of matters
which. have been• rolled about by the agency of the water.
Hence, therefore, the disturbances which have taken .place in
stratified rocks, have been occasioned by the upheaviug motion
of the igneous' roeks•which have shot up through the aqueous
rocks- tt, this• manner to such a height, as to form mountains of

extreme elevation.
The very term stratified carries an hypothetical idea along
with it, that the -rocks. defined as strata- have all been deposited
by water. Strata, however, are great beds or masses of rocks,
whose upperriaostsand,undermost surfaces form parallel planes,
varying in thickness according to the nature of the surfaces
yapoa which-they have been deposited. It is- very rattily. that
we meet with horizontal-strata- in nature, they are geaeraily.in-
clined in various-- directions at' certain, angles to the horiaon,
which aee easily ascertained.. This inclination is called their
(lip. The stratification of the secondary and tertiary forma-
tions which represent the newest of the• uppermost rocks, is
exceedingly distinct,. but that, of hindermost. rocks is not so,
owing to the influence which the heat of the igneous rocks has
bad upon it.- They are not, however, so indistinct as to be un-
observable.to a-scientific eve. There is a variety of undoubted
evidence to prove that the stratified rocks were originally de-
posited-in a- horizontal position. That they were farmed under
water is rendered, clear, for . the fact- of rounded pebbles, sea
shell and marine plants being found in them, and the position
of these fossils. with respect to the parallel surfaces of the
strata are such as to have no doubt of their having been de-
posited when the strata-were lying horizontally. That.the
mation of the stratified rocks was gradual and of greater slow-
.nees, is. proved by the successive, colonies- of shell fish that we
find in the same stratum, as well, a 3 by the different layers of
conglomerate with which it likewis‘% abounds. Thus, sup-
-posing wriver in the'summerto bring down fine sand. to theses,
and in winter when. its tempestuous current .was stronger,. small
pebbles,, it is evident that in the course-of -years we shnuld.have
successive layers of the fine sand and pebbles at the bottom.of
those streams where. the rivers deposited their contents. In
France there. is a-deposit of what is termed Indusial lime-stone,
in a district which was formerly the site of a fresh. water
lake? the, thickness of which is, very great. The,. forma-
tion of. this limo stone must have, been exceedingly . slow,
as it is entirely composed of the skeletons of minute insects.
!The formatien of strata• is going. on at the _present period,
the ocean being the receptacle of- the materials for future rocks.
The Adriatic sea was lately sounded by a continentalphiloso-
pher, and its upper surface found to consist of loose' fragments
nfenrals, shells, attd orustacea; the whole mixed with fine mud
and sand.. At the- top this was-loose and soft, but at the depth
of a foot or two it was as hard as 'any roek., This shows that
'at the bottom of the Adriatio the formation of solid rocks is
going on at the present moment. The greater number of our
sand-stones are nothing more or less than the remains of pre-
viously existing rocks which have been worn down and their
detritus carried to the sea and formed into other rocks. The
Various strata, however, have been deposited in a very loose
state over the channel of the ocean.., They are merely sand or
clay which have been deposited by the storms. It now be-
comes our duty to inquire what has been the means of changing
the soft mud. or sand into the. present hard and compact rocks.
A great many (muses, have, no doubt, been in operation to pro-
duce such great changes, one of the most powerful of which, in
all probability, is the pressure of the ocean. Now in some
places, according to Laplace, the seeis about 12 miles in depth.
'The pressure occasioned by a column of water of -this length
would be sufficient,. Without any other aid, to compress the sand
into the hardest stones. Of this Braman's press affords a prac-
tical instance. Scoresby, in his account of the whale-fisheries,
gives a striking instance of the powerful pressure of water at
a-comparatively short depth from the surface. /V boat engaged
in the whale.fishery was taken down by a whale in its sudden
descent, after being harpooned. Upon-the subsequent capture
of the whale the boat was recovered, hut found to be totally
useless for- any of the pot-poses to which wood- is applied. , So
powerfully was it compressed, that it could neither float in the
water, be burned, or he' cut with-an axe. Another very power-
ful agent in solidifying rocks, is volcanic heat. Carbonate of
lime has been, another active instrument in consolidating rocks-,
particularly in volcanic countries, where thermal springs are
of frequent occurrence. Calcareous depositions are common
in this country. When water contains any carbonate or sul-
phate.of lime in-solution, it is commonly called; hard. -The lec-
turer here shewed a beautiful specimen of calcareous deposition
which had been brought from Italy by Mr,R. V. Yates. The
carbonate of lime had deposited itself upon a number of matted
sticks which, upon decaying, had left the carbonate of lithe of a
cellular 5 tructure. Silica being soluble in water, by some pro-
cess of nature, has also assisted in uniting rocks. Iron exerts a
wonderful power in the solidification of red sand-stone. It is
well, when we have- natural- instances- on a small scale before
us, of the operation& which have taken place in nature on an
extensive scale, to avail ourselves of them. The lecturer here
shewed a nail which had heen.immersed in the bay of Dublin
for some time, and having corroded and oxydized in the water,
had united itself with the surrounding.pebbles, so as to convert
the whole into one solid mass. This is an exceedingly common
and most beautiful illustration of the mode in which a great
many sand-stones have been cemented together. Another very
curious mode in which rocks are units4.is one which-we would
not expect. When silica, in- a minute- state of division, meets
with clay or an oxide of iron, it combines with it, and forms a
very hard silicate. Common mortar is merely 'a. silicate of alu-
mina and lime. It is not a. carbonate. This is of very great
importance in architecture. For instance, the Roman mortars
were celebrated for their hardness. Wherever the Romans
went, they always found rood mortar. The grand reason of
this was, that, they procured' the best and• finest sand they could,
and stirred the mortar for a long time, so as intimately to mix
the silica and the lime. Now the same, no doubt, frequently
occurs in nature, and although it may*seem a curious fact to
notice, we find, that in the best Roman mortar, the quantity of
lime is far more than the carbonic acid could possibly saturate,
and, consequently,-that the greatest portion of it has been con-
verted into a silicate, and not a carbonate. Such, then, is an
exposition of the modes in which rocks become solidified. Some-
times only one of the causes may be called into action,- and it
is the business of the geologist by analysis to determine what
the solidifying principle is.
Strata being thus funned, we shall proceed to another branch
of the subject. We find a great number of strata perfectly ho-
rizontal, but this is far from being universally the case;- indeed,
in some instances they occur perpendicularly ' - and it has been
previously proved, that all the stratified rocks were deposited
horizontally, we arrive at a most beautiful and important fact
in geology,- that the changes which have- taken place in the his-
tory of our planet have not always been slow, but violent and
unequal. All the stratified rocks of the Alps, the Andes, and
the Himalayas; were originally deposited at the bottom of the
sea in an horizontal position,. although they are now in numer-
ous instances met with upon. their edges. We have in this
country instances of the same strata lying horizontally on one
place, and upon their edges in another. We often find that the
strata on one side of an igneous rock would- join the strata• on
the other„t has showing that the rock has-been upheaved through
the strata. It is perfectly clear that those strata which are the
nearest to- the bottom of the sea are first deposited. The upper-
most of the stratified rocks are certainly the- newest, the under-
most must be the oldest, because; they have been deposited suc-
cessively one above another in order.
When strata are parallel to-each-other, whether perpendicu-
larly or horizontally, they are said to be cenfermable to each
• other, that is, to havebeen formed during one, epoch or period
of rest. But where horizontal strata rest upon perpendicular
strata, they are said to be unconformable one to another, that-
is, to have been formed at- different. periods. Besides these,
• there have been disturbances of another kind. Rocks have
been subjected to a great variety of merhaeicatvioiences, by
which they have been curved and contorted.- They have been
subject to what are- Called fractures and dislocations. These,
in some cases form rock faults. They occur very abundantly
,in our coal- mines, and perform a very important part in them.
'The contortions of the, strata are accounted- for by supposing
the rocks subjected at the same period to a variety of pressures.
• Sir James Ball ascertained, that, by putting layers of cotton
and linen clot h- upon a table with a book upon them, and then
• applying pressure to each side, he could produce appearances
•of a similar kind to those observed in nature. Sometimes we
find Contortions on a'gigantic scale spread -over the face of a
country forming mountains and. valleys. Ma.ny beantiful in-
staeces of this occur in Kent, and they are very common in the
centre of England-.
-Artesian wells present a variety of useful phenomena, and a
knowledge of the principle upon which they depend may be the
means of produciny, much happiness. For instance, there are
many portions of the world, such as the great desert in Africa,
apparently destitute of water, in which Artesian wells may in all
probability be found of utility. These wells are formed by a
porous stratum, being included between two impermeable ones.
Thus, suppose the uppermost and lowermost of. three strata to
be composed of clay, and the central stratum of gravel, the
rain would collect in the central layei, and the strata which
covered it being punctured,- would- gush up with some force to
the surface of the earth. For instance, in London, when we