Canterbury and Westland. 287 



is to say, the whole has a thickness of more than 3000 feet. 

 Towards the Ashburton, the succession of the streams is not so 

 well shown ; but on the northern flanks of Mount Somers, where that 

 fine mountain falls in some localities abruptly for more than 1000 feet 

 in almost perpendicular cliffs, their position, nature, and succession, 

 are well exhibited. Some of the coulees, occasionally of great thick- 

 ness, have a more trachyfcic structure towards the centre, whilst the 

 smaller ones are generally more hyaline, or at least felsitic, usually 

 with selvages of pitchstone on both planes. In fact they may fairly be 

 compared to lava streams of the present day, showing the same process 

 of cooling, although, owing to different circumstances and mineral ogical 

 constituents, the magma out of which they originated naturally 

 assumed different forms. 



Examining the mineralogical structure of the acidic rocks in the 

 Malvern Hills, we find that one of their principal characteristics, both 

 in the porphyries as in the pitchstones belonging to them, is the 

 occurrence of crystals of garnets of the red variety called almandine, 

 as well as grains of bluish translucent quartz, both of which are seldom 

 absent, being enclosed in a felsitic matrix. These series are most 

 largely developed in several well-defined peaks and ranges, such, 

 as High Peak, Phillip's Eange, Eocky Range,- Rocky Peak, Mount 

 Misery, etc. ; also the lower portion of the Rakaia Grorge gives 

 a capital insight into their characteristic features. They overlie 

 not only the palaeozoic rocks, through which they have broken, but 

 also, the melaphyres on the partly decomposed surface of which 

 they appear in many localities. They have a longitudinal extension 

 from west to east, dipping mostly towards the south, but have in 

 some localities an anticlinal arrangement where they appear on both 

 sides of the melaphyric centre. They rise to an altitude of 3019 feet in 

 High Peak, the highest summit of the whole system, and the principal 

 centre of eruption, but they have suffered considerable denudation in 

 that portion of the country now occupied by the broad valley of the 

 Rakaia. In their eastern portion in Mount Misery and Mount 

 Pleasant, where they assume sometimes tabular forms, and are of 

 g~eat thickness, they overlie exclusively the palaeozoic sedimentary 

 rocks, but this contact is generally hidden by younger beds. In the 

 western ranges, however, the said contact is clearly exposed in many 

 beautiful sections, showing that they repose either on the melaphyres, 

 or often directly upon the sedimentary palaeozoic rocks. Following 

 the contour of the former, they are often only 30 to 40 feet thick, as 



