88 Transactions. 



• 



Our examination of the coast-line between Wanganui and the Wai- 

 ngongoro has now proceeded far enough to allow, us to discuss various 

 geological theories in the light of the facts that have so far been disclosed. 

 We have now traversed the coast-line for nearly the whole distance of fifty 

 miles, and the following opinions appear to us to be well established : — 



(J.) The series of rocks represents a period of continuous marine 

 deposition. 



(2.) The climate during this period of deposition was at no time colder 

 than at the present, but, on the other hand, during the greater 

 part of the time conditions were distinctly more genial. 



(3.) There is no evidence of any sudden addition to the marine molluscan 

 fauna whilst the deposition was in progress. 



(1.) The first of these opinions has to be supported from the palaeonto- 

 logical, stratigraphical, and lithological facts that have been observed. 

 From the palaeontological standpoint the evidence at first sight seem? to 

 be in favour of a decided break between the faunas of the two extremes — 

 Castlecliff and Whakino. So greatly do the faunas in these two localities 

 differ from one another that any geologist who saw the Castlecliff fauna 

 at one time and that of Whakino- Waihi near Hawera at another, without 

 examining any of the intermediate localities, would unhesitatingly come 

 to the opinion that they represented different geological periods. It 

 is, of course, true that several identical species occur in the two 

 localities ; but it is also true that the dominant species in the one 

 locality are either absent from the fauna of the other or are there 

 reduced to an insignificant proportion. Collections that have been 

 made, at intervening points, from two of which we have already 

 published lists, show, however, a clear connection between the two 

 divergent faunas. We have found no locality where the change in 

 the faunas is so marked as to prove that there is a break in the palaeonto- 

 logical succession. The locality that we have found to be most suggestive 

 of such a break is at a point three-quarters of a mile to the south of 

 the Nukumaru boat-landing. Here we have found the last specimens 

 of Melina zealandica, Lutraria solida, Ci/therea enysi, Lucinida levifoliata, 

 Mesodesma crassa, and Strathiolaria frazeri. These species, however, do 

 not all disappear at the same horizon, but in a thickness of rock that 

 measures about 100 ft. There is also the additional fact that the horizon 

 in which all these species occur contains also as many as 76 per cent, of 

 Recent species, and the fauna is clearly related in the most definite manner 

 to that in the series of rocks that lies above it. For these reasons we do 

 not regard this horizon as indicating in any sense a palaeontological break. 

 On the other hand, there must be a most definite reason for the important 

 faunal change which is so conspicuous at this horizon. It is our belief that 

 this change is due to climatic conditions, or, at any rate, to a most important 

 change in the temperature of the ocean-water which washed these shores 

 at that time. The species that continued to exist after this time were, 

 however, as varied, and indicate a temperature of- sea-water at least as high 

 as that of the present Cook Strait. We are inclined to think — though on 

 this point there is room for much divergent opinion — that, on the one hand, 

 the Waipipi series and the Whakino series contain a fauna that is, from 

 the percentage of Recent species, and from the very nature of the fauna, 

 perhaps equivalent to the Upper Miocene of Europe ; but since it is probable 

 that in an isolated country like New Zealand faunal change was relatively 

 slow, it is undesirable, at the present time at least, to place much reliance 



