250 DR. C. CHILTOJS ON THE SUBTEEEANEAN 



loose sand and shingle in their beds, and go to supply tlie subterranean waters. The 

 Canterbury rivers are so rapid and so frequently in flood that they are continually washing^ 

 away parts of their beds, and thus opening up a way for the water to escape through the 

 loose shingle thus exposed, and there is no opportunity given for such openings to be 

 permanently closed by the finer sediment brought down by the rivers. It frequently 

 happens that in the bed of the river Eyre, some five or ten miles above East Eyreton, 

 towards the source of the river, there is a considerable quantity of water, while the 

 whole of this, except of coiu'se that lost by evaporation, sinks into the ground before 

 Eyreton is reached, so tliat there the river-bed is quite dry. 



The subterranean Avatcrs, instead of being evenly spread over a whole district, often no 

 doubt form more or less distinct streams, and probably different streams arising from 

 diifei'ent sources may be found one below another ; thus Mr. Smith says that in the 

 sections of the Canterbury Plains exposed at the mouths of the llangitata and Ashburton 

 rivers, siibterraneau streams may be seen to flow out at various heights in considerable 

 volume and force. These difl'erent streams are no doubt separated by harder and more 

 impervious strata, and they will have different sources ; some of them will, perhaps, 

 obtain their supply of water from the leakage that takes place at the foot of the hills 

 owing to the break of the continuity of the strata of the plain. 



In his Presidential Address to Section E at the Christchurch Meeting of the 

 Australasian Association, Mr. G. S. Griffiths [52] has given a number of facts about the 

 subterranean waters of a part of Australia which it will be interesting to compare with 

 what we know of those of Canterbury. Speaking of the artesian weUs which are being 

 sunk on the back blocks from the centre of Queensland doT\Ti towards the mouth of the 

 Murray, he says : — "The chief sources of these water-supplies must be looked for in the 

 great eastern cordillera, which sheds the surface streams that also cross Riverina. Along 

 its crests the rainfall is of course greatest, being from 20 in. to 10 in. per amium iu the 

 Queensland portion ; and it is near to the long ribbon-shaped region of heaviest rainfall 

 — that is, along the sides of the watershed — that the superficial deposits, being largely 

 composed of gravel and rock debris, are most pervious. Further, the continuity of the 

 strata of the plains is broken at the hill-foot, where they die out against the outcropping 

 rocks of the main range, and this line of break affords to the water flowing down the 

 hills a ready passage beneath the sediments of the plains. 



" Under these circumstances a large proportion of the rain caught on the ranges leaks 

 under the subsoil directly it falls, and it flows to the sea slowly indeed, but with its 

 volume undiminished either by the evaporation which lowers the surface waters of the 

 Riverina G ft. per annum, or by the demands of vegetation, which are much greater upon 

 river-water than the public has any idea of. 



" As these subterranean waters travel away from their sources they must thin out. . . . 

 But it apjiears to me that in every district of any size there must be decider channels in 



that ancient land-surface which is now the bed-rock or reef of the miner 



" These underground watei'coiu'ses, or, as the miner would describe thein, these wet 

 leads, will run out into the plains for greater distances than a hundred miles. Indeed, 

 when we remember that the streams are undiminished by evaporation or the demands of 



