Speight. — Geological Excursion to Lake Tekapo. 41 



at the lower margins of the hollows, simulating terminal moraines of the 

 glaciers which once filled them. 



A most beautifully developed corrie, fully a mile broad, occurs at the 

 head of Stony Creek, a western tributary of the Macaulay. This is headed 

 by a well-marked amphitheatre or cirque with stoop rock walls ; at their 

 base are hollows now occupied by small ponds or swamps, the remains 

 of old corrie lakes. The lower part of the basin was once filled by a 

 deposit of Tertiary sands and clays with coal, but a great part of these 

 has been removed, so that now there is a double basin inside the limits 

 of the corrie. On the lower side, too, below the spot where the coal has 

 disappeared, there is the characteristic rock barrier, breached at one point, 

 and through this opening, in a deep narrow notch, the stream draining the 

 basin now flows. Before the coal-measures had been removed it must 

 have presented a thoroughly typical example of a coomb or corrie. 



Stratigraphy. 



The great mass of the mountains of this region consist of greywackes, 

 argillites, and slates of the Maitai series, to which may be assigned a 

 Trias-Jura age. This time classification is based almost entirely on the 

 similarity of the lithological character of the rocks to those with undoubtedly 

 Trias-Jura fossils. This is, however, supported by the author's finding 

 a fragment of dark-coloured argillite in the high country between the 

 Godley and Macaulay Rivers which shows the unmistakable sculpture of 

 Monotis salinaria. Not only the primary and secondary ribs occur, but 

 also the peculiar and regular cross-sculpturing, so that the author has no 

 reasonable doubt but that it belongs to that important Triassic fossil, and 

 the find thus confirms the age of the beds as deducted from their litho- 

 logical character. The finding of this fossil, and other finds reported lately 

 from Arthur's Pass and the Hawdon River, suggest a wide extension of 

 rocks of this age over the mountain region of Canterbury ; but it must not 

 be inferred that all the rocks of that area are of the same age. The 

 presence of heavy bands of conglomerate containing pebbles of greywacke, 

 in close proximity to beds with these fossils and in apparent conformable 

 relations, suggests that there is an older set of beds in the region of similar 

 lithological character which have furnished these pebbles, and therefore 

 lying unconformable under it. The contention of Hutton and others 

 that two distinct series of rocks occur in the mountains of Canterbury is 

 apparently correct, but much mote field-work will have to be done before 

 they are definitely separated. 



On the east side of Lake Tekapo, especially in the Richmond Range, 

 the rocks show a submetamoiphic facies ; and slaty shales with a somewhat 

 lustrous surface occur, and in all probability they grade into the true 

 phyllites exposed near Fairlie on the flanks of the Hunters Hills and in 

 the Kakahu Gorge, which rtsemble closely the phyllites of that belt of 

 Otago east of the schists. I have been informed by Mr. Pringle, owner 

 of Richmond Station, on Lake Tekapo, that marble occurs just over the 

 divide to the east of the lake, on the Rangitata slope ; and if the identifi- 

 cation of the rock is correct it means that the metamorphic belt extends 

 much farther north than has been recorded previously. Much less is 

 known of the geological features of the western side of the Rangitata 

 Valley than of any part of Cancerbury, so that the occurrence of marble 

 may well have escaped observation. The beds to the north and east of 

 Tekapo have, according to the observations of the author, a general 

 north-and-south strike, with directions west of north occurring freely. 



