The geology of the Geraldine subdivision sheet district

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Wellman, H.W. 1953 The geology of the Geraldine subdivision sheet district. Wellington: DSIR. New Zealand Geological Survey bulletin 50 72 p.

Abstract: The area geologically described and mapped includes the whole of the Geraldine sheet district (S102). It lies entirely within the Canterbury Land District and extends from the east coast of the South Island just south of the mouth of the Rangitata River west to the foothills of the Two Thumb Range, a high range that projects south-eastwards from the Southern Alps. The underlying rocks play a clear part in determining the physiography. Three physiographic units are recognizable : the foothills of the Southern Alps; the Tertiary Hills; and the Canterbury Plain. The foothills of the Southern Alps, composed of indurated but jointed sandstone and mudstone (commonly termed greywacke and argillite), form the highest part of the area described. A younger and more varied group of beds, the Tertiary strata, which once extended over the whole, have been removed from the higher parts and now crop out as low hills around the margins of the foothills. Although softer than the undermass, they are more variable in their resistance to erosion, and some beds can be traced by the ridges they form. The Canterbury Plain is composed of unconsolidated gravels worn from the Southern Alps and deposited as huge alluvial fans that lap over and around the Tertiary hills, and extend with gradually decreasing slope to the Pacific Ocean.