Speight. — Geological Features of Chrisfchurrli Arfrsian Area. 421 



attaches to this tract of country is not one of economical character alone, 

 since an accurate examination of it may throw some light on the structure 

 of the Canterbury Plains, and indirectly on questions of more theoretical 

 interest, such as the cause of the Pleistocene glaciation of this country, 

 which has lately attracted so much attention. The amount of evidence to 

 be considered is very great, as no part of the earth's crust in New Zealand 

 has been more thoroughly explored than this area. The number of wells 

 already sunk extends to thousands, and of late years all well-sinkers in 

 the transaction of their calHng, in order to be able to give accurate estimates 

 of the cost of sinking in various localities, have kept detailed records of 

 the wells they have sunk, and made careful note of the depth of water- 

 bearing beds, the amount of water obtained at certain levels, the nature 

 of the strata encountered, and the thickness of the beds. 



The records of various well-sinkers have been placed at the disposal of 

 the present author, and every assistance in the way of information has been 

 given when it has been asked for. The writer wishes especially to thank 

 Messrs. J. Osborne and J. W. Home for assistance in this respect. It has 

 thus been possible to examine the records of more than five hundred wells, 

 so that an accurate conspectus can be obtained of the whole water-bearing 

 area. 



General Structure of the Canterbury Plains. 



The detrital deposits of the Canterbury Plains have been laid down on 

 a basement rock of uncertain character, but there is evidence which 

 suggests that the same formations as occur in the western part of Canter- 

 bury are continued beneath the plains to the eastward, and extend under 

 the sea towards the Chatham Islands. The greywackes and slates of the 

 Southern Alps outcrop again near Gebbie's Pass, on Banks Peninsula ; and 

 the Chatham Islands are formed of schists analogous to those of Westland, 

 overlaid by Tertiary limestone and volcanic rocks, the former of which can 

 be correlated with limestone of Miocene or Oligocene date in the main 

 islands of New Zealand. 



The only evidence of the structure beneath the sea which stretches 

 from the Chathams to Banks Peninsula is that afforded by the collections 

 of the steam-trawler " Nora Niven " when carrying on an experimental 

 cruise on behalf of the New Zealand Government. As recorded in a note 

 to a previous paper by the present author, the trawl brought up from 

 a nimiber of stations parallel with the coast-line, and in depths of between 

 20 and 40 fathoms, pieces of brown coal sometimes as large as an ordinary 

 travelling-trunk. It is hardly credible that these could have dropped from 

 passing steamers, seeing that brown coal is rarely if ever carried by sea, and 

 it is impossible that they could have been brought down by rivers from the 

 coal-seams that occasionally outcrop on their banks, since such pieces would 

 be rapidly reduced to powder and become indistinguishable among the other 

 detrital material. It must be concluded, therefore, that the coal has been 

 derived from an outcrop on the edge of a submarine escarpment which 

 runs parallel to the coast and with its beds probably dipping west. These 

 may continue westward, and, passing under the plains, junction with the 

 coal-measures which fringe the eastern flank of the mountainous district 

 of Canterbury. The beds would then take the form of a synchne, sUghtly 

 tilted towards the east, with its eastern wing depressed beneath sea- 

 level. Further, they may form part of a great ge-syncline or synchnorium 



