頁二第張六第日六月十年酉己曆買 WAH KIU YAT PO
EXO英文中學會考試題預習專欄
·灣堅運英文書院主編導
地理科
GEOGRAPHY (2)
A) Read the following au
Source materials.
Pebbles
Sand
Mud
(-)
Grain S120
2.om
1-0.06 am
0.06 0.002 mm
(1) account for the rormation formed sedimentary rocks.
(i) attempt a classificati
or muonanica SLY
of addimentary rookE 8 to their grain eiza.
socording to
Ana (1) Sedimentary
are composed of fragments and particles derived from older rocka and carried by currents of water or air
to a body of standing water, a valley floor, or s low plain where the particles become subject to the processes of compaction, Dementation and hardening, so that eventually they become solid rocke. Three principal Sub-divisions of sedimentary rocks can be made on the basis of the origin of the rock particles
(1) Mechanically formed sedimentary rocks.
(eg sandstones, clay, and shales)./ [11) Organically formed sedimentary rocks.
fe.g, chalk, limestones, and coal) III). Chemically formed sedimentary rooks.
(e.g. rock salt, gypsum, and limestones }
Mechanically formed sedimentary rocks are derived from rock fragments produced by rook weathering, the mechanical breakup and chemical decay of rocks exposed at the lang surface. The rock fragmente thus obtained · may be swept up by running water or by wind to remote territories, all the sediment eventually finds its way to the sea, where
on a "deposited in layers. As time goen
compaction due to the weight of the over -lying Layers above which couples with the cementation of fine particles together by silicate and calcium carbonate will form "solid rook.
MHGEN OF MECHANICALLY FORMED SEDIMENTARS ROCKE
[PASITION.
boulders
rebbles
GRAIN SIZE DECREASES
AWAY FROM THE SHOR.F
GROSION
Although sedimentary rocks usually contain particles of several different grades and not all of one size, le.g. conglomerate may n contain: a fair proportion of sand or silt) it Qab be classified according to the predominant size of the particles of which they are composed.
VARIOUS TYPES OF MECHANICALLY FORMED SEDIMENTARY ROCKS
Chaw" materiale
ウ
-To certāls
銀日橋華
六期星日五十月一十年九六九一展公年八十五國民華中 育教僑華
育敎僑華
Itent, this statement may seen. To bighest mountain ranges in the be true. Toe.
Alpe world, elg the Himalayas, Rockies, snd the Andes are formed in the Alpine Perion (about 40 million years' befora presant). Bowever there are also fold mountains besidem the above mentioned ones, and auch mountaino hoclude the Scotish Highland and the Applachian These mountains which were formed anibe Caledonian Period (330 million years befor resent) are lower in elevation and lese ogged than the Alpine fold mountains. Due to the fact that they came into existence for longer time than the alpine fold counfoide, nerafore, they are subjected to the actions of various agents of weathering and erosion for a such longer time
Consequently the young fold mounta108 2160 Buffered comparatively small amount of weathering and erosion will form the digbeer
DAAKS Wloe world
STACE
FOLO MOUNTAINS
(317 There are many theOT198 MDich tried te explain the origin of the world's fold mountẹin ranges but among these there are only three acceptable theories and these included
8) Thermal contraction theory.
b) Sub-crustal convection theory, and
Continental Drift theory.
(a) THE THERMAL CONTRACTION THEORY» tries to
"explain the formation of fold mountains in)
terms of contraction of the earth's crust due zo unequal rate of cooling experienced in She crustal region, the mantle, and the gore, It 19 argued that cooling of the Berthie layers (e. crust, mantle, and core) nas took place ever since the earth
formed. The rate of cooling differs from.. layer to layer. The crust has the highest rate of cooling since it is exposed to the atmosphere and the core remains to be in molten form even up to the present time, The unequal rate of cooling would lead to the formation of wrinkles on th
the earth's surface and it is believed that such wrinkles are in fact fold mountain ranges. One of the objections to this theory is that fold mounteane, if indeed they were formed in this manner, should occur all over the surface of the earth instead of concentrated. an certain areas onlyi
FORMATION OF ROLD HI BY THERMAL CONTRACTION
O
WRINKLES DUE TO CONTRACTION WOULD. FORM FOLD MOUTAINS MANTLE
OUTER:
INNKR
CORE
OCEAN
MOUNTAIN
STAGE, MWO
(a) THE CONTINENTAL DRIFT THEORY: This ineory was proposed by a German scientist called Wegener. He believed that formerly the earth was composed of one large continent only. Later on due to earth movements the continent began to break up into several pieces. As the continents drifted apart fold mountains would formed along their leading edges since they encountered the
t amount of friction with the muntis beneath. This theory 16 all the more convincing if we took a look at the similarity an a coastline long africa and South America- which would fit in to one. anotper_like_6"jig-Baw puzzle..
The Theory of Confmentar Dift. (After Wegener")
Stage One
Stage Thre
RELATIONSHIP BETWEEN FOLD MTS & VOLCANOES
Scree
Pebblos
Sand
Smit
Clay Hud
Consolidate Rocks
Breccia
Conglomerate
Grit
Sandstone
511tazone:
muda tone, Snake
Angular rock fragmente derived from frost action.
Sedimentary rocks: With the Largest grain 8120-10 known as conglomerate or brecola. Their grain size being in the region of 2 mm. Conglomerate is formed by cementation of pebbly deposits or gravels. The term braccia 18 given to cemented deposits of coarse angular rock fragments.
Sandstones are composed of materiais, wito grain 81se between 1-0,06 mm. Sandstone and siltstone are composed of sand and wilt particles respectively" Sandstone graine may be composed of any hard inerale which in most cases would be quartz.
The
Mechanically formed sedimentary rock that nas finest grain size 18 known sa shule. The rock foretag partioles are compacted, under great pressure and is composed of clay and mud In Bong Kong. can find
hele in Peng Chau Mire Bav!
B)(1) "The highest counts109 10 the world are sl80. the youngest Discuse thie statement Account for the formation of fola mountainoj Outline the characteristica: associated with
young fold mountain range
With the vid of a world map, describe the world distribution of young fold mountain ranges.
SUB-CRUSTAL CONVECTION CURN N'T THOAY this theory was proposed by fix 125 British geologist called Arthur holmes. suggested that there are convectionel Currents operating inside the thre Interior due to temperature difference The core region would send up convectional Currents to the mantle since the forme` ` which is in molten stage has a higher temperature than the latter. The Sub- crustal currents would exert a compression as well as a tensional force on the crustél region and so the continental surface is pulled up by the compressional forces to form fold mountain ranges.
DENT.MY FECHTON CURRITS
COMPRESSION
The is
Characteristips of young fold mountains i (a) Young fold mountains are usually arranged: in parallel manner and often attain a very great neight. (e.g. Mt. Everest 29,300 ft. Andes 23,500. et:)
(b) Since the young fold mountains Buffered a shorter period of weathering than the old fold mountains, therefore they are very rugged and sharp peaks are common- (c) Folding of the crustal region not only
resulted in the formation of fold mountains but also led to the development of fractures in
in the crust which provided line. of weakness for the molten material from the earth's interior to escape to the surface. Consequently, active volcanoes are found side by side with the young fold mountain ranges. (e.g. in the Andes, the Indonesian Island Arc)
WORLD DISTRIBUTION OF YOUNG FOLD "MI
Young fold mountain ranges
(iv) From the accompanied map, one can see that
the distribution of the world's fold mountain ranges is very uneven. Most of the world's
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