Nature’s Changes in Franklin County.

Franklin Times, Volume XXV, Issue 63, 4 June 1935, Page 4

Nature’s Changes in Franklin County.

STORY OF BOMBAY. WHAT GEOLOGY SHOWS. VOLCANO, RIVER, LAVA FLOWS. “When Bombay was Young ' might well be the title ol' the address delivered by Professor J. Barlrum and Mr W. .1. Branch, at the Royal Society's conference in Dunedin, for it deals with the geology of that region, and explains why the country, as it is seen to-day, lias adopted its present lorin, says a Dunedin paper. liappy Valley is included in the survey. Botli 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 oilier approximately north-north-east. Along these there have been considerable relative movements of a major block of earth, which at its westernmost fracture bounds the lowlands of Papakura and Bombay from the upland area further east, leaving a very sleep mountain face to this latter. Near Bombay and Pokeno the clear-cut nature of this face is masked by great masses 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 om at Ararimu, which, encircled as they are by mountain rims, are difficult of explanation by ordinary stream 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 ot 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 of hills.

“Attention may be ! called to a remarkable boathook bend of the Wai,roa River where it turns north-west into the high lands at the 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 southeast 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 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 north-west became thoroughly effective. A small stream had led out into and largely clearedthe lava that blocked the original out- | let gorge of the Wairoa, into Pokeno j Valley, and now it drains paid of Happy : Valley. j “Co-ordinated with the effects on j the Wairoa of the tilting of this earth : block are similar ones shown by two J other streams further west which have j left parts of their ancient valley as • what are called ‘air gaps,’ which are' valleys devoid of any through stream. Coal Abounds in District. “The solid geology is not of particu- , lar interest to llie layman, except that I 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 cominer- ; ; cial possibilities, and, further, gener- j ; ally contained impressions of leaves j J which in some places are beautifully ; preserved. Here and there they con- , : tain extinct fresh water mussel shells of large size, entirely different from : j anythnig known in New Zealand to- 1 day. The lavas' of the area have j commercial importance for roading .

purposes, and an important quarry has been opened up not far from Rarnarama. Again of commercial inter- ■ est and of possible future importance are deposits of-manganese ore, located about six miles east of Bombay. It : 4 is understood that>a “Shipment of this •fhas already’ 1 hjeefi spot ijo Japan.”