Haast,—On the Geological Structure of Banks Peninsula, 501 
these two European voleanie mountains, will be found to possess their 
systems of dykes developed in the same manner. During a number of 
years, it has been well ascertained by me that the dykes radiating from the 
several centres of eruption situated not far from each other, continue in 
many instances without notable interruption from the former mouth of the 
erater to the outer slopes of the caldera, where they disappear below the 
sea, or under the deposits now forming the Canterbury plains, Very often 
the principal dykes rise nearly 2,000 feet above the sea level. They are 
well visible from the harbour to the summit of the rim of the caldera wall, 
above which, in some instances, they stand prominently as a wall, often six 
or eight feet high. Where proper measurements of the same dyke can be 
obtained for a long distance, it has been found that generally, as it advances 
towards the outer circle, it diminishes in breadth; however, in other 
instances this is not the case, as repeatedly I have found some which, after 
narrowing on their outward course, considerably enlarge again before 
reaching the foot of the caldera. Thus to give a few examples, the large 
dyke of trachyte, which is crossed in the railway tunnel, about 29 chains 
from the Heathcote end, is first seen west of the town of Lyttelton, near 
Naval Point, where it is nearly 40 feet thick. On the summit of the 
caldera wall, not far from the top of the Bridlepath, it has narrowed to 23 
feet 9 inches, after which it gradually gains in proportion, so that in Thomp- ` 
son’s quarry it has enlarged to 26 feet, a breadth which it still has in the 
tunnel, A mile beyond the quarry the spur along which its course can be 
followed runs out in the Heathcote valley, where it disappears below the 
Loess. 
Two remarkable dykes, reaching the summit of Dyke Hill, about 2,000 
feet high, west-south-west of Castle-hill, are very conspicuous. They both 
project boldly from the mountain, with a space of 35 feet between them. 
The eastern one is 18 feet, and the western 12 feet broad. Two similar 
dykes exist on the opposite side, and run up the caldera wall behind Rau- 
paki. To mention a few others, there are some important dykes south of 
Dyer’s Pass, which, after crossing Manson’s Peninsula, are again met with at 
Ohinitahi (Governor’s Bay), and of which several, after ascending to the very 
summit of the caldera, reach to the foot of the peninsula near Cashmere, 
being extensively quarried in different localities along their course. These 
dykes, like many others which cross the caldera wall towards the Canter- 
bury plains, mostly all radiate from a point lying in the centre of the bay, 
formed by Manson’s Peninsula on the one side, and Potts’ Peninsula on the 
other, both of which consist of quartziferous porphyries, and between which 
this newer focus has been formed after the greatest portion of the caldera 
wall had already been built up. There is also the large dyke which crosses 
