Uttley. — Tertiary Geology, Otiake River to Duntroon. 151 



block mountains of South Canterbury, and close to the base of which the 

 Waitaki River is now flowing, was diagnosed by Cotton on geomorpho- 

 logical evidence as a fault-scarp. The occurrence of these steeply dipping 

 Tertiary beds at the base of the scarp confirms Cotton's view. This 

 isolated patch of Tertiaries evidently rests on the toe of the splinter 

 described by Cotton (1917b, p. 432). The surface of this splinter is a 

 " fossil plain,'' and shows few signs of erosion. Although the Tertiary 

 rocks that formerly covered it have been almost completely stripped, a 

 small remnant has been preserved at Station Peak, close up to the fault- 

 scarp at the back of the splinter. McKay collected fossils from these 

 beds, and states that " in this section the Hutchinson's Quarry beds do not 

 present their usual characters, and must be considered as merged in the 

 Otekaike limestone " (1882a, p. 65). He further adds that " the lowest 

 beds seen are limestones as pure as, though less fossiliferous than, the higher 

 part. Upwards these beds pass into clay-marls resembhng the fossihferous 

 Pareora beds." There is no doubt that McKay collected his fossils from 

 the upper portions of the calcareous rocks at Station Peak, and that these 

 fossiliferous rocks are underlain by a much less fossihferous limestone. As 

 has been shown above, the limestone at Otiake and Otekaike is also 

 capped by a development of very fossiliferous beds, and it has been pointed 

 out that these beds are probably widely extended beneath the gravel 

 deposits of the Maruwenua tableland. McKay's collection from the beds 

 at Station Peak were determined by the late Mr. Henry Suter. Of the 

 thirty-one species specifically determined, nineteen occur in the Otiake beds 

 at Otiake (Trig. Station Z). Of the remainder, ten species are common 

 Awamoan fossils, Lima lima (L.) is Recent, and Ancilla subgradata (Tate) 

 is apparently not found elsewhere. Further, ten of the species have never 

 been found below the Hutchinsonian-Awamoan horizon of North Otago. 

 These fossiliferous beds are almost certainly at the horizon of the Otiake 

 beds (Hutchinsonian-Awamoan), lying above the main body of limestone 

 of the Waitaki Valley. 



V. Structure of the Area. 

 A fuller description of the structure will be given in a later paper after 

 the area north-west of the Otiake River has been discussed. A fault 

 (Wharekuri-Otekaike fault) is clearly defined by the outcrops of the basal 

 quartz-grits, lying close to the base of the mountain-front, as shown on 

 the map ; whilst another fault, trending north-easterly, runs north-west 

 of the conspicuous ridge extending from Black Hill as far as Ben Lomond. 

 The geological evidence for the latter fault is clearly indicated by the 

 outcrop of tilted quartz-grits and limestone at intervals at the foot of the 

 scarp, ant b)^ the occurrence of the same beds on the back slope of the 

 tilted block to the south-east. The majority of the streams draining this 

 portion of the back slope flow in an easterly direction and are consequent 

 on the deformation. These streams have stripped the Tertiary beds from 

 the higher country in the vicinity of Ben Lomond, and the surface here 

 exhibits the characteristic features of a tilted " fossil plain." Towards 

 the Maruwenua River the plain disappears beneath the Tertiary basal 

 grits and overlying beds in the basin of the stream. From Black Hill to 

 Black Point the structure of the Tertiary Rocks is synclinal, indicating that 

 the great Kakanui tilted block (Cotton, 1917a, p. 279) has in this locality 

 been warped or folded. The Wharekuri-Otekaike fault forms the north- 

 easterly boundary of the elevated block known as the Kurow Mountains. 

 The south-easterly boundary of this block is a well-marked narrow 



