Speight. — The Tertiary Beds of the Trelissick Basin. 339 



coal. These strike along the creek to the north-east, and dip north-west 

 at high angles — over 60°. In the Thomas River, below the junction with 

 Moth Creek, occur sandy clays and shales with bluish greensands striking 

 almost east and dipping north 65°, practically along the line of the Thomas 

 at that part of its course, the strike of the beds swinging round in conformity 

 with the direction of the limestones on the northern part of Castle Hill. 

 Below the road-crossing the direction is also easterly, with northerly dip ; 

 but as the stream is followed down it gradually changes till the exposures 

 near the mouth of the river are reached. Owing to the cover of slip 

 accumulations from the high unstable terraces and river-banks, and the 

 covering of grasses and soil, the exact sequence cannot be determined. 



In the upper part of the Thomas River, close to the roadman's cottage, 

 the higher members of this series are developed. They consist of shales, 

 sandv clays, greensands, sulphur sands with occasional beds of impure coal 

 in the lower part but with occasional interstratined layers of conglomerate 

 in the higher portions, and thin bands of lignite. They dip up-stream — 

 that is, to the west — at angles varying from 20° to 30° ; some of the vari- 

 ation may, however, be due to slip, and their total thickness must exceed 

 500 ft. It is important to note the occurrence of the pebble beds at this 

 stage, as thev are found not only in other parts of the Castle Hill Basin 

 but widelv distributed throughout North Canterbury towards the close 

 of the Tertiarv series, and in perfect conformity with the underlying 

 fossiliferous beds. They are specially well seen at the mouth of the Wai- 

 para, in the Mount Grey and Mairaki Downs, and up the Okuku River, 

 and indicate the presence of land of considerable extent in close proximity 

 to this region at the close of the Tertiary era. 



In the Hog's Back Creek itself the higher members of this series of beds 

 are exposed. At the mouth green sandy shales occur, and above them 

 white sand ; but the country is much slipped, and no good sections are exposed 

 for some distance up the creek, where the directions of the beds are involved 

 with the folds which have affected the limestones to the north in the vicinity 

 of Waterfall Creek. However, they seem to conform to their direction. 



In a small tributary on the south side of the Hog's Back Creek the beds 

 strike north, and dip to the west at an angle of 35° ; but at the mouth of 

 this small creek they apparently have a strike which runs west of north : 

 this may, however, be the result of slip. Half-way up the main creek 

 there is exposed an impure lignitic sandy shale with a N. 70° E. strike and 

 a dip of 30°. to the south ; this overlies a blue sand weathering brown. 

 Farther up still, the beds strike east by north and dip south at 60° approxi- 

 mately, the beds consisting of white sand and sandy clays, the creek 

 following along the strike, These beds are succeeded again by con- 

 glomerates with pebbles of greywacke, representing the highest beds 

 exposed in the series. 



At the point where the creek flows past the end of the Hog's Back 

 it is impossible with the limited exposures to make out the relations, but in 

 all probability the beds are pinched in, taking the form of a completely 

 closed syncline, with the small outcrop of limestone noted previously as 

 the western limb of the fold. On the other hand, they may be faulted 

 down. On the west of the Hog's Back Ridge the fragmentary shell beds 

 occur resting quite conformably against the limestone where it dips at 

 high angles, but there is no exposure of the higher beds. In Waterfall 

 Creek, too, there is a small exposure of the greenish sands in the S3 r ncline 

 which terminates the limestone ridge. 



