672 Transactions. — Geology. 



carried by a few rivers to the sea and taking this as the index- 

 standard by which to provide a time-measure for estimating 

 the age of the earth is by no means satisfactory. No ac- 

 count appears to have been taken of the power of ice as a 

 denuding factor within the arctic regions, and, as far as I am 

 aware, no one has ever attempted to glean information as to 

 breakaways and land-shps which take place within specified 

 areas. Both of these are aspects of denudation which cannot 

 be overlooked in formulating an index of past time as esti- 

 mated in terms of denudation. The lowering of a river-basin 

 necessarily modifies the rate of flow, and the carrying capacity 

 varies in proportion to the lowering of the basin by means of 

 land-movements of all kinds. The east-coast district of this 

 island extending from Cape Turnagain to East Cape, a dis- 

 tance of about three hundred miles, will illustrate what I 

 mean. 



This district is bounded towards the west by the Eua- 

 hine and Eaukumaru Mountain-ranges, and embraces an area 

 of 8,970 square miles, or 5,740,800 acres. The counties in- 

 cluded within this area are Patangata, Waipawa, Hawke's 

 Bay, Wairoa, Cook, and Waiapu. The land is mostly hilly, 

 and the rocks abutting on the sea-coast belong mainly to the 

 Later Secondary and the Older Tertiary formations, and are 

 made of stiff blue clays, marls, sandstones, with here and 

 there indurated limestones. In the interior the rocks belong 

 to the Younger Tertiary group — shingle, grits, clays, and lime- 

 stones predominating. The average rainfall for the whole 

 district is about 40in., being less along the coast than towards 

 the uplands in the west. The rainfall, however, is a varying 

 quantity, and appears to increase and decrease in regularly- 

 recurring cycles of from six to nine years. Thus, in 1866 

 there was a deficiency of rainfall in the district of 7"2in. ; in 

 1872, or six years later, the deficiency was 13-32in.; in 1878, 

 or six years later, the deficiency rose to 16-16in. ; and in 1886- 

 87, or eight years later, the deficiency was actually 20-26in. 

 The years of diminished rainfall were followed by years in ex- 

 cess of the average, some years showing a large increase, whilst 

 others approached the normal standard. In 1892 the average 

 rainfall was more than reached, but in the two succeeding years 

 the rainfall exceeded all previous records, more particularly in 

 1893, when more than 60in. of rain fell over the entire district. 

 Now, 40in. of rainfall spread over the district under notice 

 represents 5'6 cubic miles of water. This water disappears 

 from the land by river-drainage, by percolation, by evapora- 

 tion, and by the demands of vegetation. During years of 

 shortage the rainfall was dimmished by one-third the normal 

 quantity, which means that about 3-7 cubic miles of water fell 

 instead of 5-6 miles. In years of excess the quantity was 



