The presence of intrusive rocks in the Kaikoura Mountains has been known for many years. McKay (1886, 1890), in his pioneer reports on the geology of this extensive region, gave a fairly detailed and at times graphic description of the occurrence of these igneous rocks, but did not concern himself with their petrology except to tag them with names based on macroscopic appearance. Thomson, thirty years later, was obviously impressed by their abundance and variety and wrote a brief paper on their microscopic petrology (1913); this was apparently intended as preliminary to a detailed account, but later he devoted himself to the stratigraphy of the region and his monographic paper (1919) does not contribute further to the earlier description of the igneous rocks except to discuss their distribution and age relations. Since Thomson's work nothing has been added to our knowledge of these rocks save for the description of an analcime-tinguaite pebble from the Wairau Bar, probably derived from this region (Bartrum, 1936), and some details regarding the occurrence of igneous rocks in the northern foothills (King, 1934).
My interest in these rocks was aroused while I was working on the igneous rocks of the Mandamus-Pahau area in North Canterbury in 1944 and 1945. It was evident that the intrusive rocks in this area showed marked resemblances to those described by Thomson from the Kaikouras, seventy miles away to the north-east. During the following years a number of trips were made to investigate the distribution of intrusive rocks throughout this region. In November, 1944, I journeyed from Hanmer to the Clarence-Acheron junction, up the Acheron River to its junction with the Guide, thence through Bullock Head Gully to the Dillon River, up the Dillon, across the upper reaches of the Tweed River, past Lake McRae, and down the Elliot River; return was made by the same route, except that the Dillon was followed to its junction with the Clarence, thence up the Clarence to Jollies Pass. In February, 1946, the lower part of the Middle Clarence Valley was examined, by following the pack trail from Kekerangu to Coverham, thence up the river to Quail Flat, and out to Kaikoura by way of the Seymour and Kahautara Rivers. In February,
1954, the Clarence River was traversed by canoe from its junction with the Acheron to the mouth, which enabled the examination of the streams rising from the ranges on either side of the valley; at the same time a detailed traverse was made of the Muzzle River, which was clearly a major source of the igneous rocks in the river gravels. In April, 1954, a brief visit was again paid to the lower part of the Middle Clarence Valley to examine the igneous rocks in the Swale and Mead tributaries, and a rapid trip was made up the Awatere Valley as far as Upcot to determine the distribution of intrusive rocks in this area.