NATURE'S CHANGE

Auckland Star, Volume LXVI, Issue 124, 28 May 1935, Page 9

NATURE'S CHANGE

STORY OF BOMBAY.

WHAT GEOLOGY SHOWS

VOLCANO, RIVER, LAVA FLOWS

(By Telegraph.—Press Association.)

« DUNEDIN, this day. "When Bombay was Young" might well be the tide of the addres* delivered _ by Professor J. Bartruin and Mr. W. J. ' Branch, at the Royal confer- ( once in Dunedin, for it deals/!with the geology of that region, and explains why : the country, as it is eeen to-day, has adopted its present form. I Happy Valley is included in the suri vey. Both are in the Franklin County. . ."It is an upland area," says the paper, "Hilly in relief, bordered by great earth ' fractures running in two series, one north-north-west and the other approximately north-north-east. Along these there have been considerable relative mvements of a major block of earth, which at its westernniost fracture bounds the lowlands of Papakura and Bombay from 'the upland area further cast, leaving a very steep mountain face to this latter. Near Bombay and Pokeno the clear-cut nature of this face is masked by great massed of volcanic lavas, which have been outpoured from near Bombay Hill." / Another remarkable /fracture can be traced from Maraetai, on the Hauraki Gulf, through the great gorge of the Wairoa River past the well-known Wairoa falls at Hunua, and then along the extraordinary intermontane plains called Happy Valley to the outlet gorge of the Mangatawhiri Stream. Geographic' Problems. "The major interest of the region lies in its geographic, problems. Besides the cup-like hollow of Happy Valley, there are several others, such as the Hunua basin and a similar one at Ararimu, which, encireded as they are bv mountain rims, are difficult of explanation by ordinary siaeam erosion. There are also many indications of extraordinary stream drainage. For example, Happy Valley is now drained by three streams, one flowing to the north-west to join the Wairoa River, which enters the Firth of Thames, another flowing to the Mangatawhiri Stream and thence to the Waikato, and still another joining the drainage of the Pokeno Valley, These last two streams breached the very lofty range cf hills. "Attention may be called to a remarkable boatho'ok bend of the Wairoa River where it turns north-west into the high lands at tlie back of Hunua; and there is no doubt that at one time the Wairoa itself flowed along Happy Valley to join the Waikato. Its flow was obstructed by the fact that the block of country over which it was flowing to the south-east was slowly tilting north by earth fracturing in operation, so that it found difficulty in maintaining its course. Finally its waters were captured by another stream, which had worked its way from near Clevedon along a shattered belt of country, following the I great fracture referred to previously. Wairoa River Blocked. "Part of the blockage of the Wairoa in its south course was due to the outpouring of volcanic lava, which flowed down its original outlet valley and blocked it, so that temporarily the Wairoa spilled over a low saddle a little further east and entered temporarily the Mangatawhiri River, near the mouth of its outlet gorge. Subsequently, however, the capture of its waters from the northwest became thoroughly effective. ' A small stream had led out into and largely cleared tlie lava that blocked the original outlet gorge of the Wairoa, into Pokeno Valley, and now it drains part of Happy Valley. "Co-ordinated with the effects on the Wairoa of the tilting of this earth block are similar ones shown by two other streams further west which have left parts of their ancient valley as what are called ' air gaps,' which arc valleys devoid of any through stream. Coal Abounds in District. "The tiolid geology is not of particular interest to the layman, except that it may be mentioned that workable coals exist at Bombay and near Drury, as well as in the Hunua region and elsewhere, and that the fireclays associated with the coals have commercial possibilities'., and', further, generally contained impressions of leaves which in some plages are beautifully preserved. Here and there they contain extinct fresh water mussel shells of large size, entirely different from anything known in Xew Zealand to-day. The lavas of the area have commercial importance for roading purposes, and an important quarry has been opened up not far from Ramarama. Again of commercial interest and of possible future importance are deposits of manganese ore, located about six miles east of Bombay. It is understood that a shipment of this has already been sent to Japan."