422 Transactions. 



extending over tlie whole area from the Alps to the Chatliain Islands, with 

 schists outcropping on its eastern and western visible limits. 



The uncertainty of the soundings between Banks Peninsula and the 

 Chathams renders it impossible to speak definitely of the form of the sea- 

 bottom in that region, but it appears from the few that have been obtained 

 that the sea gradually deepens for about forty miles, to the 100-fathom 

 Une. and then suddenly drops to over 1,000 fathoms, a depth which is main- 

 tained to the vicinity of the Chathams. WTiether this is part of a submarine 

 plain or a portion of a fold valley which runs in a north-easterly and south- 

 westerly direction parallel to the coast of the North Island is at present 

 uncertain, and it is hoped that the efforts being made in Wellington to get 

 a line of soundings run from Lyttelton to the Chathams may be successful, 

 as it will throw considerable light on the evolution of the main crustal 

 features in this region. 



That a syncline exists involving the Cretaceous coal-measures, and 

 probably the overlying limestones, seems to be very reasonable, but the 

 cause of its form is uncertain. It may be due to deep-seated movements 

 of the earth's crust, of which we can say little at present, or it may be 

 due to loading caused by the immense quantities of detritus poured into 

 the sea by the great Canterbury rivers. The presence of a line of earth- 

 quake origins parallel to the coast-line of the plains suggests crustal 

 movements along a. line in the neighbourhood of the probable submarine 

 coal-outcrops. 



Source and Character of the Material out of which the Plains 



ARE constructed. 



The detrital matter out of which the plains are constructed consists 

 chiefly of shingle with an admixture of sand and silt, the whole being formed 

 from the weathering and disintegration of the greywackes out of which the 

 great mass of the Canterbury mountains is formed. In the higher parts 

 of the plains, near the base of the mountains, there is a considerable mixture 

 of angular matter and large siibangular blocks, but in the lower parts of the 

 plains the gravel becomes much smaller. The fragments are usually from 

 2 in. to 4 in. in diameter, and rarely exceed 8in. ; they are well rounded, 

 and seldom exhibit the flattened ovoid form produced by the incessant drag 

 of the backwash on a beach subject to heavy seas. It cannot, however, be 

 inferred with certainty, because the pebbles on the plains are usually of 

 such equilateral dimensions that they must have been formed wholly by 

 river-action, as the shape of a pebble on the beach is primarily determined 

 by the shape of the block from which it has been derived. On examining 

 a beach of limestone pebbles on the north side of Amuri Bluff, I was struck 

 by the frequency of the cricket-ball size and shape, and this could only be 

 due to the orighial fragments having been cuboid in form. The angular 

 Iragments produced by the disintegrating action of the frost and other 

 agencies on the moinitains of Canterbury are usually of equilateral dimen- 

 sions. However, on examining the beach at Birdling's Flat, between Lake 

 Ellesmere and the sea, it will be noticed that a very large proportion of the 

 pebbles exhibit the true shingle form as distinct from gravel. If the plains 

 had been formed by marine action they must have been subject on their 

 eastern margin to attrition by the same heavy seas that sweep up the present 

 Ninety-mile Beach, and therefore beach-shingle should form a large part 

 nf their material. As this is not the case, I think it mav be inferred that 



