376 Transactions. 



Outpourings of rock of identical lithological character occur in other 

 localities of the Canterbury Province— e.g., at Malvern Hills, Eakaia Gorge, 

 and Mount Somers — and it is only by reference to them that we can fix 

 the age of the Lyttelton rhyolitic eruptions. The evidence for the period 

 of the former is as follows : In these localities rhyolites lie invariably on an 

 eroded surface of Jurassic strata, while over them lie coal-measures con- 

 taining the following fossils : bones of Ichthyosaurus, shells of Inoceramus, 

 Conchothyra parasitica, Trigonia, belemnites. The fossil-content of these 

 beds fixes them as Cretaceous. At the base of this series He a conglomerate 

 formed largely of rhyolitic pebbles and beds formed of detrital matter of 

 rhyolitic origin, so that the rhyolites formed a land surface in Cretaceous 

 times. However, at Rakaia Gorge and at Mount Somers coal-seams occur 

 interbedded with rhyolitic tuffs, from which it is evident that eruptions 

 were taking place while the coal was being deposited. It seems certain, 

 therefore, that the rhyolite eruptions took place at the close of the Cretaceous 

 period on the margin of the mountain region of Canterbury ; and, although 

 it is not safe to draw inferences as to age based purely on lithological resem- 

 blance in the case of volcanic rocks separated by a distance of forty miles, 

 it is the only evidence that we have to rely on at present, and therefore 

 we may say, at least tentatively, that the age of the Lyttelton rhyolite is 

 Cretaceous also. 



3. Second Volcanic Phase. 



(a.) Lyttelton. 



The second phase of volcanic activity was marked by the pouring-out of 

 basic lavas which built up the Lyttelton and Akaroa cones. Structurally 

 they are both composite cones of the normal type, as can be seen from the 

 magnificent sections afforded by the sea-cut cliffs. It will be best to con- 

 sider first of all the case of Lyttelton, as it is more easily examined, not 

 only because roadmaking and excavations are more common near the 

 centres of population, but because the Lyttelton Tunnel has been driven 

 in a radial direction through the wall of the cone, and records of the in- 

 clination of the flows and samples of the various rocks encountered were 

 made by Haast,* and a petrological description of these rocks is given 

 by Filhol.f These show that Lyttelton has all the features of a com- 

 posite cone built up of layers of lava and fragmentary material, the latter 

 being thicker as the interior of the volcano is approached along the line 

 of the tunnel. Judging from the quaquaversal dip of the flows observed 

 on the cliffs and on the sides of the deep-cut valleys, as well as from the 

 records of the tunnel, the centre of the harbour corresponded to the centre 

 of activity, but owing to the occupation of the bottom of the crater by 

 the sea the site of the actual vent cannot be definitely located. It can 

 perhaps be fixed with reasonable certainty as a deduction from the orienta- 

 tion of the dykes which traverse the walls of the crater-ring. Their arrange- 

 ment is markedly regular, and when they are plotted they are found, witli 

 few exceptions, to radiate from a small area just south of Quail Island, 

 which may therefore be regarded as the actual centre of disturbance and 

 the precise locality of the vent. 



The exposed limits of the rocks of this series to the north and west of 

 Lyttelton Harbour are easily determined, seeing that they continue down to 



* J. von Haast, loc. cit., p. 355. 



t H. Filhol, Mission de Vile Campbell, Geologie, 1885, p. 66. 



