Sessional_Paper_1926 — Page 81

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quence is at all possible, and even in these there are other factors that would render such a possible flow of little value except at low levels in their immediate vicinity. The localities referred to are (1) the valley north of the Pat Sin range between Fan Ling and Sha Tau Kok, and (2) the valley that forms the northerly extension of Castle Peak Bay, between Castle Peak Farm and Cheung Kong Wai. In both cases the flow, if encountered, would not be large, and could only be tapped near the valley floors, from which it would have to be transported by pumping.

ANY TYPE

ROCKS OF

ARTESIAN WELL

EFFECTIVE HEAD OF ARTESIAN

FLOW

SURFACE PROFILE

•

SHALE BEDS

IMPERVIOUS

TO WATER

BEDS OF SAND- SFONE READILY

POROUS TO WATER CIR- CULATION AND

STORAGE

NOTE:-Water will flow freely from the well to a height less than that indicated as

Diagrammatic profile to illustrate artesian flow and

the principles on

it is based.

which

Arrows indicate direc- tion of flow of water,

"effective head."

Tunnelling, Reservoir Construction, Side-Hill Construction.

In these three, and many similar, operations, there is scope for the skilled applica- tion of geological principles. In the selection of sites, the kind of rock, its structure, fracture system, state of decomposition, uniformity or heterogeneity of grain and mineral composition, presence or absence of dykes or shear zones, are very important considera- tions from an economical standpoint. While the geologist cannot guarantee the fulfil- ment of underground forecasts or programmes that he makes, nevertheless he can, by securing their adoption,' greatly reduce unnecessary expenditure, eliminate many chances of failure, and prevent "wild cat" financial exploitation.

With reference to side-hill construction, such as large buildings and retaining walls, the geological investigation made by the writer at Po Hing Fong following the disastrous collapse of July 17, 1925, revealed the fact that such a rock as the Hongkong granite is a source of weakness rather than stability under conditions of tropical weathering, and should be so considered in the matter of foundations and heavy superstructures. Its relatively easy decomposition to a slippery buff-coloured clay permits the formation in it of planes or surfaces of slipping parallel to the hill slopes, on which landslides may readily occur.

Report and Map.-The completion and publication of the geological report and map of the Colony will portray and discuss much more thoroughly the areal distribution of the rock formations with their lithological characters, and present more complete data. concerning potential mineral resources.

W. L. UGLOW,

Geologist to Hongkong Government,

21st April, 1926.