346 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [JuTlG 19, 



often of good quality (Browncoal). They are again overlain by thick- 

 bedded calcareo-arenaceous strata, called by Dr. Hector the Oamaru 

 series, and are broken through by newer volcanic rocks, mostly 

 dolerites, sometimes forming large sheets, and with palagonite 

 tufas associated with them. These are again covered by sands, clays, 

 &c., and some small beds of shell-limestone, probably of Pliocene age. 

 These Tertiary rocks appear either on the slopes of the lower range, 

 on the eastern or western side of the Southern Alps, or they form 

 small isolated hills in front. Otherwise they are mostly concealed 

 by the great Pliocene alluvium forming the Canterbury plains on 

 the eastern side, through which the present watercourses have cut 

 deep channels on the higher or western portion, whilst near the sea 

 they have covered them by recent deposits, of which I have given 

 a description with sections in my Eeport on the formation of the 

 Canterbury plains. 



It is often in the deep gorges where the rivers leave the mountains 

 that the Tertiary rocks are well exposed. 



Banks peninsula is a volcanic system of some complication. The 

 two larger harbours, Port Victoria and Port Akaroa, are true Cal- 

 deras formed by doleritic rocks, consisting of lava-streams and agglo- 

 - meratic and tufaceous beds derived from them, of the succession and 

 structure of which the railway-tunnel between Lyttleton and Christ- 

 church, crossing the Caldera-wall of the former, offers an excellent 

 and very instructive section. Between these two Calderas a large 

 volcanic cone, now partly destroyed, has been raised by trachy-dolo- 

 ritic and andesitic lavas, while the last centres of eruption are 

 apparently two islands in the middle of the two older Calderas, con- 

 sisting of a number of basaltic lava-streams having a columnar struc- 

 ture. On the western side of the peninsula w» meet a large zone of 

 quartzose trachytes, which seem to have made their appearance after 

 the doleritic and before the andesitic lavas. 



I shall return to this interesting subject after the railway- tunnel 

 has been completed. 



III. MOEAINE-ACCFMTJLATIOKS OF THE POSTPLIOCENE OR GlACIAL 



Epoch. 



I have not as yet alluded to the extensive morainic accumulations 

 found on both sides of the Southern Alps, as I wish to call especial 

 attention to them in treating of them separately. The eastern 

 glacier-beds are extensive, and reach to a much greater distance 

 from the summit of the central chain than those of the opposite side, 

 but they do not descend to such a low position. 



Owing to the remarkable steepness of the western slopes of the 

 Southern Alps, these Postpliocene accumulations reach the sea-level, 

 for more than fifty miles covering the country uniformly with their 

 stupendous masses. 



This is quite in accordance with the relative position of the pre- 

 sent glaciers on both sides, of which I shall give an example. 

 The great Tasman glacier, the largest in New Zealand, about 16 



