WoRLEY. — On the Geology of Nelson. 419 



out of the solid rock by the action of the river, two forcible 

 questions present themselves to the mind : First, what has 

 become of the material which once filled the valley from crest 

 to crest of the existing hills? Second, how long did it take 

 the river to remove that enormous mass of matter? The 

 answer to the first question is comparatively easy. The 

 matter thus eroded has been carried down to the sea, the 

 lighter particles floating far out into deep water, and there 

 settling down to form fresh deposits of sedimentary rock, 

 while the heavier portion would settle at the mouth of the 

 river, and there form a delta. Beneath our feet at the pre- 

 sent moment lies the debris of the rocks which once formed an 

 integral part of the mountains near us. The greater part of 

 the Town of Nelson stands upon the delta of the Maitai, while 

 the delta is still extending seaward by fresh accumulations 

 brought down by every flood. In the same way the Waimea 

 Plain has been reclaimed from the sea by materials brought 

 down from the hills by the Rivers Wairoa and Wai-iti. The 

 second question, ' ' How long did it take the river to erode the 

 valley?" cannot be answered definitely, but an approximation 

 may be made. By calculating the amount of sediment held 

 in suspension by several rivers, and by taking into account the 

 rate at which they flow, it has been found that a river lowers 

 the area of its basin about 1ft. in two thousand years. Not 

 knowing the mean depth of our river-basins, I am unable to 

 make any estimate upon this basis ; but by making the most 

 liberal allowances, in a rough guess, at least hundreds of thou- 

 sands of years would be required for the formation of many of 

 our valleys. 



Thus far I have dealt almost exclusively with the geology 

 of our own immediate neighbourhood. The fear of making 

 this paper too long prevents me this evening from touching, 

 even in barest outline, on the interesting geological facts 

 connected with the Owen, the Wangapeka, the Baton, the 

 Takaka, and the Collingwood districts. I shall therefore close 

 this paper by a brief reference to the minerals of economic 

 value found in the provincial district, mentioning, as I pass, 

 the geological formations to which they belong. First in 

 importance are the coal-deposits. The coal-deposits of New 

 Zealand belong to the Cretaceo-tertiary formation. In this 

 respect New Zealand differs widely from other countries, where 

 coal is usually associated with rocks of Carboniferous age. 

 The Cretaceo-tertiary formation comes between the Miocene 

 rocks of the Port Hills and the Triassic rocks of the Wairoa 

 Gorge. Its principal areas of development may be seen by a 

 glance at the map, where the parts coloured green indicate the 

 presence of Cretaceo-tertiary rocks. These coal-deposits must 

 in the future prove a source of great wealth to the district. 



