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Since thei r formation , ove r 6 5 millio n year s ago , th e rocks which make up Cape d'Aguilar, hav e been subject t o erosion and weathering. Younger, later deposited rocks have been stripped off and the intrusive granodiorites and rhyolites brought to the land surface by erosion of the rocks into which they were intruded. One o f th e mos t dramati c physica l change s t o hav e occurced over geological history is the fluctuations in sea level, even i n relativel y recen t times . I n ver y recen t geologica l history, the earth has been in the grips of an ice age. Although during this time Hong Kong was not covered by ice, the region did experience th e effects o f this event. Growth o f massive ice sheets, both land glaciers and sea ice, locked up immense volumes of water at the poles, thus causing a global fall in sea level. Such a fall exposed more land, which would then have been subjected to aerial erosion and weathering processes. In the las t ten thousand years , with th e waning and retreat of the ic e sheets, the frozen wate r has been released back int o the se a and, globally , sea levels have risen . In Hon g Kong , sea level has risen by over ten metres in the last ten thousand years. Thi s ris e ha s not , however , bee n relentless , rathe r involving periods of regression as well as transgression. The las t rise in sea level flooded rive r valleys, hilltops being isolated as islands. Everywhere this can be seen in Hong Kong; projecting headlands embracing shallow embayments and numerous, 235, offshore island s and islets. Ten thousand years ago, Tai Tarn Bay would have been a much shallowe r estuary with extensive mudflats, mangroves and salt meadow flanking a stream meandering between the Stanley and Cape d'Aguilar peninsulas. The area now occupied by Lobster Bay would have been low lying land, which has since been flooded. An aerial photograph of the area of the marine reserve taken in February 1963 (Plate 11) shows that where the Swire Institute of Marine Science now stands, there was a platform, Plate 11 . An aerial photograph of Lobster Bay taken in February 1963 showing that prior to any construction the intertidal platform sloped gently from east to west. At the top of the photograph can also be seen th e Bokhar a batter y (Courtes y o f the Surve y an d Mapping Office of the Hong Kong Government). bounded t o th e nort h an d sout h b y the stee p granodiorit e cliffs an d slopin g gently downward s fro m th e eas t t o west . This i s a tru e intertida l platform , ove r which , hig h wave s approaching from the east would wash to drain into Lobster Bay, particularl y durin g typhoons . Eve n today , durin g typhoons, and although the western side of the platform has been built up for construction purposes, waves still send water spilling around the Swire Institute of Marine Science building to the south into Lobster Bay. The essentia l configuratio n o f th e ti p o f th e Cap e d'Aguilar peninsula arises from the NE-SW structural tren d which dominate s th e are a and, a s explained earlier , by th e different roc k type s and thei r relativ e resistanc e t o erosio n and weathering. The majo r physica l force s actin g o n th e peninsul a (Figure 3) particularly t o the south east, are waves. On th e eastern shore of Cape d'Aguilar, the erosional power of waves has cu t bac k softe r rocks , often th e granodiorite , t o creat e fingers o f harde r roc k whic h poin t int o th e sea . Similarl y with th e tw o sea arches, softer rock s along fault line s hav e been differentially cu t away. Within Lobster Bay, erosion has polished area s of the shore. Waves, however, ar e not solel y agents o f destruction. The y ar e als o capable o f deposition , and this is most visible in Lobster and Telegraph Bays, where beach sediments accumulate. These cobble and...

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