Kermode, L.O. 1972 Poro-o-tarao tunnel. Progress geological report. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey report EG 138 23 p.
Abstract: To give a geological appraisal of the Poro-r-taroa ridge through which the railway must pass, and to assess the optimum location for designing and constructing a new tunnel and approaches that will keep future maintenance to a minimum. This report includes and modifies the findings of the previous geological reports by Hay (1.8.63), Thompson (4.5.66), and Jeune (20.2.69), and this accompanied by a map and diagrams. It summarises the drilling results from the northern portal, and gives a general description of the surface geology of the site. (auth)