Speight. — The Tertiary Beds of the Trelissick Basin. 341 



considers an unconformity necessary, but his sections, notably those on 

 pages 64 and 65 of his report, leave no doubt as to his position. His 

 representation of the block of limestone in the upper part of Whitewater 

 Creek as lying across the denuded edges of the tuffs and greensand beds 

 is decidedly open to question, and is not borne out by my observations. 

 I could find no exposures which warrant the arrangement of beds as indi- 

 cated, and the position of the limestone block is easily and more satisfactorily 

 explained by the occurrence of a fault, of which there is undoubtedly other- 

 good evidence, bounding the western side of the basin. In his section, too, 

 on page 61 the representation of the beds does not appear to be altogether 

 satisfactory ; however, he shows a perfectly conformable sequence near the 

 gorge of the Porter ; but his interpretation of the section up the Whitewater 

 has no doubt influenced his ideas of the country to the west of Castle Hill. 



On page 406 of his article Hutton emphasizes the existence of the uncon- 

 formity. His main line of evidence is that in the Coleridge Creek area 

 the lower limestone does not now exist, but has been removed by denudation 

 before the upper limestone was deposited. The absence of the lower lime- 

 stone in this area can be explained satisfactorily on other grounds — viz., 

 that it was never laid down, owing to the interference with deposition of 

 calcareous beds by volcanic action. In the upper part of Coleridge Creek, 

 more removed from the centre of activity, both beds of limestone, with 

 their intervening tuffs, are quite normally developed and are conformable 

 throughout, the whole sequence being represented. If, therefore, my inter- 

 pretation of the structure is satisfactory, there- is no reason for the uncon- 

 formity. This opinion is further strengthened by the fact that in those 

 places where the ash beds are not interstratified the lower limestone passes 

 up without a break into the upper stone, and explains why it is that the 

 lower- stone does undoubtedly in general have the characteristic coralline 

 character of the upper. They are in fact normally the same bed, and the 

 ash beds do not indicate the presence of a break. 



The unconformity which is placed higher in the sequence— that is, over 

 the upper limestone — has also, in my opinion, no foundation palaeontologically 

 or stratigraphically. As far as the last is concerned, the main evidence of 

 Hutton rests upon the disagreement in the strike of the beds in the tributary 

 of Whitewater Creek. After a careful examination of the locality I can 

 see no evidence of this ; any change in dip or strike is perfectly gradual, 

 and entirely explicable on the grounds that the beds of the area have been 

 subjected to gradual deformation. The fact that the Pareora beds rest 

 in the northern portion of the basin on the Waipara series is not entirely 

 correct, even assuming that the lower limestone is of Waipara age. In the 

 lower part of Broken Eiver, below the road and near the gorge, the sequence 

 is perfectly conformable and normal ; the same is entirely true near the 

 limestone gorge in the Thomas and Porter Rivers. The only apparent 

 discrepancy occurs near the fault which crosses the Broken River, and then 

 it is perfectly possible that outcrops may be suppressed, as so frequently 

 occurs in connection with strike faults. I do not think that this affects 

 the case as far as the contact of the Pareora beds and the limestone is con- 

 cerned, since to the west of the Hog's Back the Pareora beds lie perfectly 

 conformably on the limestone, in that part of the area there being no tuff 

 bed interstratified with the limestone, although it occurs underneath it. 

 Showers of ashes had evidently not fallen in that area while the limestone 

 was being laid down. It must be noted in this connection that Hutton 

 admits fairly the absolute conformity of the beds exposed between the two 

 limestone gorges of the Porter. 



