Speight. — Geological Feature,^ of Chrixt church Artesian Area. 427 



and finer material, with occasional peat. There is a progressive diminution 

 in the amount of gravel encountered in the bores on approaching the pre- 

 sent coast-line. This is by no means uniformly true, as the Boys' High 

 School well, in the western part of the city, shows a very large proportion 

 of gravel to be present, a feature which is also shown to a minor degree by 

 other wells in its vicinity — for example, the Christ's College, and the Ex- 

 hibition well in Hagley Park. This exception does not, however, negative 

 the statement that there is a general increase in the amount of shingle on 

 going east. These beds must have been laid down where strong currents 

 were in operation, due either to river or sea currents, the former in all pro- 

 bability ; and they are almost certainly due to the aggrading action of a 

 powerful stream on a land-surface. The presence of peat also proves that 

 subaerial conditions obtained over the area while the beds were in process 

 of being deposited. The sand and clay beds interstratified with them are 

 in all probability principally of marine origin, since remains of shells are 

 frequently encountered in them. Their association with land-beds proves 

 that there was a struggle going on between the forces that tend to build up 

 a sea-bottom to the level of the sea and to continue it as a land-surface 

 above that level, and, on the other hand, a general sinldng of the land, 

 which is evidenced by the peat-beds now found so far below sea-level — 

 600 ft. in the case of the well at Islington. It is apparent that at times 

 the aggrading forces got the best of it. How far this depression of the land 

 has gone on in excess of that already proved is quite uncertain, and onlv 

 deeper wells will disclose the information. 



The water-bearing beds of this section, as, indeed, is the case in others, 

 ^re almost invariably composed of shingle. According to well-sinkers, 

 water is frequently found all through these gravels, but the most prolific 

 supply is obtained from just above the impervious layer below the beds ; 

 in fact, its general distribution throughout the gravel-layers in a particular 

 well is looked on as an unpromising indication for a good flow being ob- 

 tained from that bed. The overlying impervious layer is usually clay, but 

 it may be sand or even more consolidated and less porous gravel. 



The height to which the water rises is generally found to increase 

 with the depth of the well, though in one or two cases the reverse is found 

 ill the case of a particular bed. This may be put down to friction prevent- 

 ing the passage of water through the bed. Owing to the level of the ground 

 ()\QY a large part of the area being only a few feet above sea-level and 

 sensibly uniform, there is apparently little difierence in the height to which 

 water rises on approaching the coast, but the condition of texture of the 

 bed appears to be the controlling one affecting the height to which wells 

 rise for a particular depth. In the part of the area to the west where the 

 plains rise somewhat steeply the wells are non-flowing, although the pressure 

 of the head maintains the water in the pipe at a fairly definite level, and 

 it would flow, if it were possible to take it ofl", below the level of the 

 ground. The water in the first stratum of the well at Islington rises only 

 to 42 ft. of the surface of the ground — that is, the level of the Avater is 70 ft. 

 above the sea. 



Series No. 2. — Beep Wells : Cenlral Ward, Christckurch. 



(Plate X.) 



This series of sections gives a record of a nimiber of the deeper wells 



of the centre of the city, with one or two others added for purposes of 



-(•(^mparison. They furnish the most detailed representation of any particular 



