DEEP LEADS OF OTAGO. TO THE EDITOR.

Otago Witness, Issue 2203, 21 May 1896, Page 19

DEEP LEADS OF OTAGO. TO THE EDITOR.

Sir,— ln the Otago Daily Times of the. 4th inst. there was a very interesting paper from Mr W. Green on the above subject. Gold miners owe no small gratitude to such an accomplished geologist for the bints he has given on miniog problem*. There are two points to which I would like to draw attention. One is the tilted strata of some of tbe auriferous deposits of Central Otago, to which Mr Green refers particularly. Professor Hutton in his •• Otago Geology," page 65, calls it the " Wanganui formation." It is only a superficial' deposit, for which there has been a difficulty in accounting for its oon' orbed structure. It is plainly a fre*h water drift, brought from distant localities. Its gravels, clays, and lignites show transportation, while same of the boulders are subangular. _ The latter fact would indicate that the deposition was contemporary with glacial conditions. To my mind the debris under review was drifted by liquified sdow or ice, »nd spread out on the enrface of the old lakes when they wera froaen to the bottom, at the points where the -streams came from the mountains. The ice beneath, during tbe accamulition and for a protracted period, was covered over by the superincumbent

mass, bnt by-and-bye the ice below was thawed, and the entire deposit falling on the sloping basement of the mountain took the dip of tbe bottom en whioh it fell. If the materials' so laid down stretched acrcs3 a frozen-over gully they would make the V-ahape indicated. We have seen this phenomenon takirg place on Scottish streams daring a severe frosty winter. Tiaat the strata have had a fall is shown by being broken at the end next the mountain. These deposits, round the Maniototo and Munuherikia valleys, have a similar deration on the mountain sides, where they were shot on to the frozen lake. Auother point is that the Tn i^eka cemt>n!s are of marine origio. This mould b-s difficult to imiutr.in. Tuaptka cementtt are a ground m iraine of a plei3fcocene glacier that descended from the Southern Alps sear Mount Cook. All . the gold and gravel* found in the la' era. l gullies have bean washed cut of this glacier bed by the present etreams. Tie glacial conditions made a great change in the courses of out O'lago rivers, and especially ou the east coast, from the CJutha to th.B Shag river. All oLthern have to a greater or lesser . extent shifted their channels. The Taieri croases the old Silvers^ream Valley nearly at A right angle, and so of the others. The deep leads must therefore belong to the older river and lako systems of Ottgo. The high river giwela, such as at Mount Burster, would be contemporary with the old lake depos ts of ' ligfite, cl»ys, and gravels of inioceno at early pliocene age which underlie the glacial aud post-glacial drift referred to, among which, wa conclude, deep lead auriferous beds maybe sought. — I am, ,&c, . „