Hill. — On Artesian Wells. 435 



Tlie flow of water fi'oiii each well is at the rate of 270 

 gallons a minute, or, say, 16,000 gallons an hour, or 384,000 

 gallons a day. Thus, these two wells, representing the 

 work of a forty-horse-power engine, supply more than three- 

 quarters of a million gallons of water daily, of exceptional 

 purity and suitability for domestic purposes. The cost of 

 sinking the two wells, including £64 for boring-tools and 

 £30 for bonuses, amounted to £534 16s. 7d., which at 7 

 per cent, interest represents an annual outlay of less than 

 £38, and for which the town is supplied with more than 280 

 millions of gallons of water ready for use. The water as it 

 rises to the surface exerts a pressure of about 131b. to the 

 square inch, corresponding to a rise, when allowance is made 

 for friction, of about 30ft. above sea-level. The head- 

 pressure exerted on the water at the bottom of the well, which 

 is 196ft. in depth, in order to raise it 30ft. above sea-level, is 

 equal to about seven atmospheres on each square inch. This 

 will show how very necessary it is when sinking a well to 

 insist upon pipes being used of the very best description, as in 

 the case of the well just mentioned the pressure upon the 

 low^est section of the pipes amounts to over 1001b. to each 

 square inch. With such a pressure it is easy to understand 

 why so many artesian wells begin to diminish their supply of 

 water after the lapse of a few years, as they become choked by 

 the rotting portions of the pipe towards the bottom of the well. 



But the sinking of the two wells in Munro Street has not 

 merely given information as to the dip and general character 

 of the beds overlying the true water-bearing bed : by the 

 " shelling-out process," which was adopted in sinking, interest- 

 ing information has been brought to light as to the age of the 

 overlying beds. This has come about by the discovery in the 

 blue-clay sands of a large number of very small shells in an 

 excellent state of preservation. The common cockle-shell 

 and a whelk had been the only shells noticed in previous 

 sinkings, but it is now known that shells are common in most 

 of the beds passed through during the process of sinking, 

 except, perhaps, in the clay-sandy bed which immediately 

 overlies the water-basin. In this bed much vegetable matter 

 is met with, but no trace of shells as far as I have been able 

 to discover, and I am inclined to the opinion that the clay- 

 sandy bed which rests upon the water-bearing basin is of 

 fresh-water origin, and, if not unconformable to the overlying 

 beds, at least represents a change in the area of deposition to 

 which reference will presently be made. The following is a 

 list of the more important shells found in the beds during the 

 process of_ sinking the wells. They were referred by me to 

 Professor Hutton, of the Canterbury College, who kindly sent 

 me the names of the different specimens received by him : — 



