Haast, — On the Geological Structure of Banks Peninsula, 601 



tliese two European volcanic mountains, will be found to possess tlieir 

 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 

 crater 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 Eau- 

 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 then- 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 



