Speight. — Terrace-development of Canterbury Rivers. 29 



(].) Evidence for a Recnet Elevation. 



The existence of peat-beds, as well as buried logs — that is. 

 an old land surface — is proved by artesian-well borings in the 

 Christchurch area. Peat has been found at the following depths : 

 at Ward's brewery, 400 ft. ; at Sydenham, 500 ft. ; and at Isling- 

 ton, 700 ft., below the surface of the ground. As the first two 

 places are less than 20 ft. and the last only 112 ft. above sea- 

 level, the evidence is convincing that the land stood at least 

 600 ft. higher than at present when the outskirts of the plains 

 were formed. This proveo a substantial elevation in recent 

 geological times ; and as artesian borings are put down further 

 a greater elevation may be proved, as only in the immediate 

 neighbourhood of the Port Hills has solid rock been reached by 

 such borings. 



Additional positive evidence of an increased height of the 

 land is to be found in the bays which surround Banks Peninsula. 

 They are all, or nearly all, drowned valleys, and were formed 

 when the land was higher. In most cases they are valleys 

 which have been formed wholly by water action. In the 

 cases of Akaroa and Lyttelton Harbours, the original craters 

 of volcanoes have, perhaps, been enlarged by explosions, but 

 certainly have been further amplified by water erosion and 

 extended into the valley form. The exposed floors of these 

 valleys grade into the submerged portion. The usual depth 

 of the bay near its outlet to the ocean is from 6 to 8 fathoms — ■ 

 that is. from 40 ft. to 50 ft. — and this gives the minimum eleva- 

 tion necessary to allow the valleys to be formed. But all the 

 bays have been filled to a marked extent by mud washed from 

 the hillsides, so that no accurate estimate can be made of the 

 depth of the rock floor beneath. Borings in search of arte- 

 sian water-supply put down in the valley behind Sumner failed 

 to reach either water or solid rock at a depth of 200 ft. 



The date of this elevation is difficult to determine in the 

 absence of any fossil evidence or any other accurate time indi- 

 cation ; but, taken in conjunction with the evidence from arte- 

 sian wells, it is, I think, of fairly recent date. Another proof 

 that the land has recently been higher is afforded by the shape 

 and position of the valleys of the streams near Timaru. In 

 most cases they are submerged where they enter the sea. 



The evidence from the valleys as well as that from the wells 

 proves conclusively that the land was recently much higher, 

 certainly as much as 600 ft. This elevation would produce 

 a great extension of the land eastward, as the sea-bottom is 

 sensibly flat till the hundred-fathom line is reached at a distance 

 of about forty miles from the present coast-line. Then the depth 

 increases very rapidly to over 1,000 fathoms within the next 



