REPORT OF THE CHIEF ASTRONOMER 341 



SESSIONAL PAPER No. 25a 



the sediment?, there is a small and apparently isolated outcrop of rather 

 coarse nionzonite like that of the neighbouring main body. Two small 

 seemingly isolated masses at least partly surrounded by augite porphyrite, 

 occur within the city limits and along the line of the Great Northern rail- 

 road near the border of the large monzonite area. Also, a tongue-like 

 extension of the monzonite is shown on the map as extending across the 

 summit of C. and K. mountain: this body is probably directly connected 

 with the main area. 



' The border of the central monzonite mass is concealed by drift along 

 the slopes of C. and K. mountain but towards the eastern margin of the 

 map, it may be seen to lie close to the contact of the augite porphyrite 

 and the area of porphyritic monzonite there exposed. From this position, 

 proceeding eastward beyond the limits of the sheet, the line of contact 

 of the monzonite with the older formations, swings around to the north 

 on the slopes of C. and Iv. mountain, which drop rapidly to the east. On 

 this eastern face above the contact of the monzonite with the augite 

 porphyrite occupying the summit of the hill, are a number of tunnels 

 commencing in the porphyrite but whose dumps are composed largely of 

 monzonite. It would seem that the porphyritic volcanic of C. and K. 

 mountain is a comparatively shallow body occupying the upper portion 

 of the hill but underlain by monzonite which, proceeding westwards, gradu- 

 ally outcrops at successively higher levels along the south face of the ridge 

 and finally occurs in what appears as a dike-like extension* across the top 

 of the hill. That is. the top of the body and a portion of the covering of 

 the monzonitic mass seems still to be preserved at this point. This idea 

 furnishes a reasonable explanation for the occurrence of the compara- 

 tively large area of the bedded series exposed in the northern part of the 

 city of Eossland within the monzonite and which probably represents a 

 roof-pendant. The same mode of origin may be true of the neighbouring 

 smaller, detached area of similar rocks and also of the two small outcrops 

 of augite porphyrite on the lower slopes of Monte Cristo, or they may 

 represent fragments torn from the formations once overlying or surround- 

 ing the monzonite. 



' The larger part of the monzonite mass lies in the valley of Trail 

 creek while its greatest extension in a northerly direction are respectively 

 up the Center Star gulch and over the low country east of the slopes of 

 C. and K. mountain. This possible connection between the distribution 

 of the monzonite and the lower lying portions of the country, may be 

 purely fortuitous but when considered in relation with the apparent capping 

 of the body on C. and K. mountain and the possible occurrence of roof- 

 pendants, it points to the conclusion that, within at least the area mapped, 

 the exposures of monzonite belong to a section near the upward limits of 

 the body. It is, nevertheless, possible that at some point or points, the 

 monzonite extended on upwards through the overlying Carboniferous and 

 probably later rocks and may have appeared at the surface as a volcano. 



