The First Period of Mountain Building

So great was the volume of spoil deposited on the shores of Gondwanaland that it caused the earth’s crust to sag. Lateral pressure on this zone of weakness then led to folding on a large scale and the uplift of an extensive mountain system. The layers of rock laid down in Mesozoic times were partly altered by this pressure, the sandstones being changed into greywackes and the mudstones into argillites—the two types of rocks which make up most of the Southern Alps. The intense folding and crumpling of rock strata at this time can be seen very clearly near Mount Cook.

Agents of erosion at once attacked the new mountains and slowly reduced them to a more or less featureless plain over which seas advanced in later Cretaceous times. From the sediments then deposited many fossils have been collected in North Canterbury, Marlborough, and Kaipara Harbour, Auckland.

During this period the ammonites, those curious relatives of the modern octopus, still dominated the seas, but their relatives, the now extinct belemnites, were also numerous. Snails and shell­fish, too, were abundant, and ancestors of the modern oyster throve exceedingly, for in parts of Canterbury their skeletons remain as massive shell-beds.

The fossil remains of these creatures suggest another interesting link between New Zealand and other parts of the world. They are very similar to those found in rocks of the same age in Grahamsland, in Patagonia, and in Chile. Since they lived in shallow water, it has been suggested that New Zealand was at this time connected to Antarctica by a land-bridge, forming a coastline along which marine life could pass to and fro between New Zealand and South America.