342 Transactions. 



i). TECTONTC FEATURES. 



The main tectonic features are those indicated in my paper on the 

 intermontane basins (p. 341), the conditions of faulting and folding being 

 those which have resulted from the settling of a block of country with a 

 consequent readjustment of the beds to a somewhat smaller area. An 

 arrangement of inward-dipping beds towards the centre of the basin is 

 materially departed from, although a cursory examination of the locality 

 might encourage this belief. The main faults (see map) which are now 

 clearly visible and affect the Tertiary beds are, — 



(1.) A fault running north and south to the west of Castle Hill along 

 the base of the Craigieburn Mountains, with a downthrow to the east, as 

 a result of which isolated blocks of limestone are left stranded at the base 

 of the range. It is difficult to arrive at a precise estimate of the amount of 

 throw, but it is certainly some hundreds of feet. The situation of the 

 stranded blocks is somewdiat hard to account for, but they may be blocks 

 which were separated from the main mass when the whole of the area was 

 faulted down, their contacts with the adjacent greywackes not being visible, 

 though the occurrence of limestone so close to the latter without any inter- 

 vening shore-line beds does certainly suggest that this is not the position 

 in which they were laid down. In the section figured in my paper just 

 cited the contact of the limestones with the greywacke to the west of the 

 Hog's Back represents a contact without indication of a fault. At this 

 spot the junction is extremely obscure, and it may be a shore-line or a fault 

 contact- — probably the latter, as this would be on the line of the undoubted 

 fault continued north from the west of Castle Hill. 



(2.) There is another pronounced fault, running north-east and south- 

 west through Parapet Rock on the main road in the direction of Broken 

 River. This is evidently closely connected with the folding of the beds, 

 and grades at both ends into folds. The downthrow is to the south-east, 

 and there is considerable lateral movement of the blocks of limestone, as 

 is evident from the brecciated and slickensided surfaces. 



(3.) Hutton considered that a fault ran from the northern end of Castle 

 Hill eastwards toward the upper limestone gorge of the Porter. This is 

 apparently of the same nature as the last, the folding at the two ends 

 being undoubted ; but the middle portion, where faulting should be 

 visible if it really existed, is covered with river-gravels and is completely 

 masked. 



(4.) A well-defined line of fault runs parallel to Coleridge Creek in a 

 north-east and south-east direction, as is evident from the stranded blocks 

 of limestone left high and dry on the north-west side of the creek : in fact, 

 the whole valley of this stream appears to be determined by an earth- 

 fracture, the later sedimentaries being dropped down and to some extent 

 pinched in between the walls of greywacke. The folding which the beds 

 exhibit is in all probability due to the folding which attended this disloca- 

 tion of the strata. This line of fault may be continuous with the fracture 

 which no doubt determined the eastern boundary of the basin, as it will 

 conform thereto with but slight alteration in direction. When this line is 

 continued to the south-east it reaches Coleridge Pass, which forms a slight 

 depression in the lofty ridge of the Craigieburn Range ; but there is no 

 positive evidence of its continuance into the basin of the Rakaia on the 

 western side of the range, although its extension in this direction is extremely 

 probable. 



