Hutton. — The Formation of the Canterbury Plains. 465 



Art. L. — The Formation of the Canterbury Plains. 

 By Captain F. W. Hutton, F.E.S. 



[Bead before the Philosophical Institute of Canterbury, 2nd November, 1904.] 



The Canterbury Plains are formed by beds of gravel, sand, and 

 day of varying thicknesses, covered in places by a layer of silt, 

 or loam, which is used for brickmaking. North of Banks 

 Peninsula the plains commence at the sea-level, but to the south 

 they show on the sea-shore a range of low cliffs averaging some 

 25 ft. in height ; so that about a mile more has been washed 

 away on the south than on the north side of the peninsula. 

 Inland they gradually ascend until at the base of the mountains 

 which bound them they have attained to from 1,000 ft. to 

 1,500 ft. above the sea-level. 



Near the mountains a few rocky islands, as we might call 

 them, rise through the gravels to the surface. Of these View 

 Hill and Burnt Hill have a volcanic origin ; the hill at the lower 

 gorge of the Waimakariri is formed of sandstones and slates of 

 Older Mesozoic age ; while Curiosity Shop, in the Rakaia, con- 

 sists of Oligocene limestones and calcareous sandstones. 



The thickness of the gravel-beds is not known. At Christ- 

 church wells have been put down to a depth of more than 400 ft., 

 and at that depth have come across deposits of wood, which 

 must be either driftwood or the remains of an old forest lying 

 where it grew. 



The origin of the stones forming the gravels is obvious. 

 Most of them are pieces of sandstone, sometimes with quartz 

 veins running through them — a rock which is abundant in the 

 mountains from which the rivers flow ; while in the southern 

 portions of the plains we also find chalcedony and volcanic rocks 

 similar to those found from the Gawler Downs and Mount Somers 

 to the Malvern Hills. Evidently the stones forming the gravel- 

 beds have been brought down by the rivers ; and this is con- 

 firmed by their subangular, or partly rounded, forms. If the 

 gravels have been brought to their present positions by the rivers, 

 so also have the sands, for they are only small fragments knocked 

 off the sandstones ; and we may say the same of the clays. Both 

 the sands and the clays are mechanical deposits which have been 

 sorted and arranged by moving water. 



There are, however, certain irregularities in distribution 

 which require careful examination — I mean the hills composed 

 of gravel which rise above the general surface of the plains, 

 such as the Moeraki Downs, Racecourse and Little Racecourse 

 Hills, and Woolshed Hill. Of these, Woolshed and Little Race- 

 course Hills are partly morainic in origin, and contain large 



30— Trans. 



