Hill. — Denudation as a Factor- of Geological Time. 673 



increased by .one-third ; or, in other words, the rainfall was 

 increased to 7*5 cubic miles. The difference between 3-7 cubic 

 miles and 7*5 cubic miles is very great, and wide differences 

 must be expected in the denuding effects which each quantity 

 of water is likely to produce when spread over the same area. 

 But even an excessive rainfall may be so distributed as to 

 time that its effects as a denuding power are but slightly 

 greater than under what may be termed normal conditions. 

 As pointed out above, it is the intensity of flow, or of move- 

 ment, that produces unusual denuding effects, and this is well 

 shown by the effects of the floods which took place in this 

 district in December and January, 1893-94. When going 

 over the district shortly after the floods had taken place, I 

 was surprised to find how much the appearance of the country 

 had changed. Thousands of breakaways or slips were to be 

 seen, some of them of large extent ; and I was impressed with 

 the absolute necessity of keeping a record of surface-changes 

 such as had been produced not so much by an excessive rain- 

 fall as by a heavy continuous downpour at a time when the 

 surface of the country was saturated. I had traversed the 

 district for sixteen years, but, although occasional large slips 

 had been met with, there had been nothing to approach the 

 marvellous changes in 1893-94, which showed in the com- 

 pletest manner how largely a district may have its surface- 

 features modified by a rainfall which represents only a slight 

 deviation from the normal conditions of that district. As I 

 did not see how to obtain the necessary information concern- 

 ing the changes brought about in so extensive a district with- 

 out a heavy expenditure of time such as I was unable to 

 afford, I communicated with Sir James Hector, the head of 

 our New Zealand Geological Department, and he very kindly 

 offered to obtain from the settlers such information as I might 

 deem necessary for the purpose of my inquiry. Subsequently 

 a circular letter was issued by Sir James, as follows: "For 

 the purpose of keeping a record of the destructive landslips 

 which took place along the east coast of the North Island 

 during the years 1893-94, holders of land will oblige by 

 filling in the queries given below, and returning the paper at 

 the earliest opportunity : 1. County and locality. 2. Owner. 

 3. Area and situation of land. 4. What area do you estimate 

 slipped away at the period named ? 5. Do you remember any 

 similar period when slips were as numerous ? 6. Give rock- 

 materials — i.e., whether clays, sands, or hard rock." It was 

 manifestly impossible to send a letter to every settler through- 

 out the district irrespective of the area of land occupied, and 

 only large holders were communicated with. In the majority 

 of cases the queries have been answered ; and I wish here to 

 express my thanks and obligations to Sir James Hector for the 

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