Superficial Geology

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and High West; granites form lower and more rounded peaks with surface boulders (exhumed corestones) more common, as seen around Mount Butler. In general the fine-grained granites are more resistant to weathering than the coarser varieties. The medium-grained granite outcrops on the Kowloon peninsula originally had a deeply weathered mantle. This provided a ready and abundant source of easily excavated fill, and facilitated the cutting of platforms. The sites of many major housing estates were formed in this way. The Geotechnical Control Office (GCO, 1979, 1984) has adopted a six-fold scheme based on that of Moye (1955) for the classification of weathered rock material. Studies for this Geological Survey by J. Ho and A. Lai (written communication) on the material weathering grade classification of the tuffs of the Repulse Bay Volcanic Group have highlighted the different weathering characteristics of the vitric tuffs of the Ap Lei Chau Formation as compared with the crystal tuffs of the other volcanic formations mapped within the district. The colour change in the vitric tuffs from black (fresh rock) to white (moderately weathered material) is particularly striking (Plate 45). Ruxton & Berry's (1957) scheme for the zonal classification of weathering profiles, despite the stated arbitrary nature of their zonal boundaries, has found favour with engineers in Hong Kong (GCO, 1979, 1984). However, this geological survey has indicated that incomplete profiles are more profound than Ruxton and Berry considered them to be. An illustration of Ruxton and Berry's scheme applied to complex weathering profiles is shown in Figure 30. The distinction between sandy superficial deposits and weathered granite is often difficult to make in boreholes. Records of boulders in the supposed basal part of a superficial sequence, may, in some cases, more properly be interpreted as indicating the presence of corestones within weathered rock profiles. ••••••••BBB Plate 56 - Pre-split Cut Slope in Medium-grained Granite Showing Incipient Corestones in Slightly Weathered Material; Hammer Hill, East Kowloon (3991 2207) Weathering mantles on the low, rounded hills of granite in northern and eastern Kowloon are commonly deeply gullied, as seen on the flanks of Hammer Hill and Diamond Hill. A striking example of such gullying in completely weathered material may be seen at Ngau Chi Wan (4024 2201, Plate 55). The vertical walls of the gully are about 3 m high and show evidence of vertical slab failure, largely governed by disaggregation (slaking) of the weathered granite as a result of groundwater seepage, rather than by basal undercutting by attrition. Adjacent to this site, on the southern end of Hammer Hill, is a recently exposed pre-split cut slope face (3991 2207) that 113
Plate 57 - Cut Slope in Medium-grained Granite Showing Zone C of the Weathering Profile Overlying Zone A; Jat's Incline, East Kowloon (4021 2293) %;SB* Plate 58 - Cut Slope in Fine- to Medium-grained Granite Showing Regular Distribution of Rectilinear Corestones in Zone C; Tai Tarn Reservoir Road, Hong Kong Island (3852 1336) 1 mp 114
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5 andKowloon Geoloovof 1:20 000 She
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Foreword This Memoir describes the
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Page Chapter 6 Structure 75 Folds 7
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Page List of Plates Plate 1 - Coars
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Plate 48 Plate 49 Plate 50 Plate 51
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Table 1 - Grain Size Description an
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TATE'S CAIRN • HO CHUNC 0 1 2 3 4
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The Present Survey Geological field
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Table 2 - Solid Rocks and Superfici
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Pumice, glass- Crystals, crystal fr
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(2) Western Hong Kong Island (4) Fe
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T-HT+T + T+T+T VT+-TV*V' YUNG SHUE
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Plate 3 - Thin Section of Lapilli-b
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Plate 7 - Coarse Ash Tuff in Tai Mo
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Details Tate's Cairn to Fei Ngo Sha
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Siu Chai Wan to Big Wave Bay. New e
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South of Rennie's Mill (4410 1760),
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Victoria Peak to Aberdeen, Mount Ca
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An extensive outcrop of Tai Mo Shan
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The field criteria used by Allen &
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dark biotite-rich groundmass. Bioti
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On Stonecutters Island the rock is
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Plate 17 - Coarse-grained Granite (
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Plate 21 - Fine- to Medium-grained
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«, , , y 25 - Megacrystic Medium-g
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with the older coarse-grained grani
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semi-liquid state. Near the contact
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along Tai Hang Road near its juncti
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1 HK4040, 2. HK4221, 3. HK4222, 4.
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follows the observed emplacement se
Page 63 and 64: The geochronology of the granites h
Page 65 and 66: Abundant Feldspar / Sparsely Figure
Page 67 and 68: Plate 30 - Quartz Syenite (HK 4019)
Page 69 and 70: Plate 34 - Thin Section of Quartzph
Page 71 and 72: in diameter. Biotite is present as
Page 73 and 74: Basalt dykes have also been noted i
Page 75 and 76: m J^TV ; Plate 39 - Pegmatite Nest
Page 77 and 78: Anticline axis Synclme axis Fault,
Page 79 and 80: Figure 17 - Circular Histograms of
Page 81 and 82: 11 NE n = 109 11 SW 11 SE n = 165 1
Page 83 and 84: East Hong Kong Island (USE). A prom
Page 85 and 86: quartz crystals in a preferred orie
Page 87 and 88: Plate 42 - Thin Section of Medium G
Page 89 and 90: gm JTM JAC VI VI ; ; II n Plate 45
Page 91 and 92: Chapter 8 Superficial Geology The s
Page 93 and 94: Clear Water Bay Road and Ho Chung.
Page 95 and 96: of Lai (1982) the Mid-levels colluv
Page 97 and 98: containing subrounded cobbles and b
Page 99 and 100: Fill The coastline and topography o
Page 101 and 102: Methods of Survey The offshore depo
Page 103 and 104: SAND/GRAVEL + Junk Bay JBS1/1A n Kw
Page 105 and 106: CHEUNG SHA WAN Figure 28 - Generali
Page 107 and 108: Particle size distribution analyses
Page 109 and 110: Plate 51 - Seismic Trace of Superfi
Page 111 and 112: Plate 53 - Seismic Trace of Superfi
Page 113: fault zone SHEET ( weatherin § JOI
Page 117 and 118: Plate 60 - Cut Slope in Completely
Page 119 and 120: MINERAL PROSPECTS AND MINOR WORKING
Page 121 and 122: altered. There is little quartz pre
Page 123 and 124: Cobbing, E. J., Mallick, D. I. J.,
Page 125 and 126: Watt, J. C. Y. (1970). A Han Tomb a
Page 127 and 128: Borehole Grid Ref. Surface level Su
Page 129 and 130: Borehole Grid Ref. Surface level Su
Page 131 and 132: Cho Yiu Chuen 41 Cho Yiu Estate 54
Page 133 and 134: Mount Butler Drive 55 Mount Butler
Page 135 and 136: Tate'sPass'30 Tau Chau 34 Telegraph
Page 137: LB 555.125 S89 Strange, P. J. Geolo
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Superficial Geology

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