Canterbury and Westland. 281 



CHAPTER VIII. 



The Melaphtbe and Qttaetzifeeotjs Porphyry Eruptions. 



Before proceediug to the next, or "Waipara formation, it will bo 

 useful to treat separately of the intervening period when a series of 

 eruptions, consisting of basic and acidic igneous rocks took place on 

 a large scale along both sides of the Southern Alps, those on the 

 eastern slopes being the most extensive. These eruptions had long 

 ceased before sedimentary beds belonging to the newer era were 

 deposited on their flanks, the material for them being generally 

 derived from their disintegration and destruction. It is impossible to 

 say, at least at the present stage of our knowledge, when the palaeozoic 

 rocks described in the previous pages were folded, crushed and 

 denuded to such a remarkable extent, or when they appeared above 

 the sea, and how long they remained above it under powerful atmo- 

 spheric influences, being subjected at the same time to erosion by 

 rivers or by the sea along the coast 9 but we can affirm with safety 

 that this period, during which they were denuded to a remarkable 

 extent, was a long one. Moreover, there is sufficient evidence to show 

 that even the forms of several of the present main valleys were already 

 indicated. Thus, when the next period of disturbance occurred, the 

 main configuration of this Island was already so far sketched out that 

 the addition of new rocks made no considerable difference in its 

 outlines. These rocks, as previously observed, consist of two main 

 groups, both of igneous origin, of which the older belongs to the basic 

 and the younger to the acidic sub -division. 



