Si'KKiHT. — (,' col ofi leal Fiiitiinx <if Clirtxl rlunch Artrxian Area. 425 



of peaty matter rarely exceeding 2 ft. in thickness. These bogs rest on 

 beds of clay formed by the sediment which has been deposited by rivers 

 and tides, but principally by the latter raising the sea-bottom to the high- 

 tide level. The area of bog and sandhill stretches back from the sea till 

 the surface gravels of the plains are encountered, which have no regular 

 boundary, but stretch out as tongues into the swamp and sandhill complex. 

 An excellent example of this is to be seen at Addington, where a shingle- 

 bank reaches down to the eastward, passes into Sydenham, and crosses 

 Colombo Street South near the Sandridge Hotel. This shingle-deposit 

 marks the presence of an old stream of gravel, and others are found in 

 many places reaching out more or less into the swampy country. This is 

 the general type of land-surface which is found all over the area. In those 

 parts 'close to the sea sandhills and peat-bogs predominate, but on going 

 away from the sea the shingle becomes more and more important, till it 

 forms the whole present surface of the country. The land in all probability 

 possessed similar surface-features when the water-bearing beds were being 

 laid down. 



General Conditions op Artesians. 



In the publications of the United States Geological Survey there are 

 numerous excellent papers dealing with the scientific aspects of the flow 

 of water in artesian wells. In one of the earliest of these, entitled " Requ- 

 site and Qualifying Conditions of Artesian Wells " (5th Annual Report, 

 1883-84), Professor T. C. Chamberlin considers the general conditions 

 which determine the occurrence and the flow of wells. Other papers of 

 great interest are those by F. H. King, on the " Principles and Conditions 

 of the Movements of Ground- water," and by Charles S. Slichter, on the 

 " Theoretical Investigation of the Motion of Ground- waters," both in the 

 19th Annual Report (1897-98). In a paper on " Rock Gas and Related 

 Bitumens " (11th Annual Report, 1889-90), W. J. McGee expresses the 

 conditions governing artesian wells so very succinctly that I quote his actual 

 words, especially as they have an important bearing on the conditions 

 governing our own wells. He says (page 603), " In the inverse order of 

 their importance, the requisites for artesian flow of water are — (1) Condi- 

 tions of structure, (2) conditions of texture, and (3) conditions of supply. 

 The most favourable structural condition is the arrangement of the strata 

 in the form of a basin, as in the Province of Artois in France, from which 

 the flowing well takes its name. The rain-water falling on the rim of such 

 a basin percolates through the strata to its centre, and there rises through 

 natural or artificial openings to a height depending upon the difference in 

 altitude between the area of supply (or catchment-area) and the head of 

 the well ; but the basin structure is not absolutely essential, and artesian 

 flows are obtained from uniformly inclined strata (such as those constituting 

 the Atlantic coastal plain) when the catchment-area is elevated consider- 

 ably above the well-head, or when the strata either diminish in permeability 

 in the direction of the inclination or extend far beyond the point of outlet 

 —i.e., textural and other conditions may combine with structure to produce 

 flow where structure alone is unfavourable. The most favourable textural 

 condition is found when the porous stratum extends from the catchment- 

 area to the part of the basin, trough, or monocline tapped by the drill, and 

 is overlain (excepting in the catchment-area) by an impervious stratvun. 

 This condition, like the last, is not absolutely essential to artesian flow, 

 since all rocks are more or less pervious, and if the difference between the 



