Morgan. — Unconformities in Stratified Hacks of West Coast. 277 



the Eocene coal-measures is doubtful ; but, in any case, the interval of 

 time represented is long. The general evident discordance in strike and 

 dip, together with the great difference in lithologieal characters between 

 the Palaeozoic and the early Tertiary rocks, renders recognition of the 

 unconformity an easy matter. Probably — in fact, certainly— some deposi- 

 tion of sediments took place between the Ordovician and the Eocene in the 

 North Westland and Westport districts ; but of this there is no direct 

 evidence, all traces of such beds having been removed by pre-Eocene 

 erosion. At Reefton, however, near the districts discussed, Devonian strata 

 are found, and Trias- Jura rocks appear on the eastern side of the Southern 

 Alps. 



It is noteworthy that though over considerable areas the bituminous- 

 coal measures were deposited on a nearly flat surface, yet in places the 

 overlap of the higher beds on the pre-Tertiary old land is considerable. 

 The nature of the basal conglomerate, and more especially of the Hawk's 

 Crag breccia, is further evidence of an irregular land -surface at the begin- 

 ning of the Eocene. Although the Kaiata beds, the uppermost member of 

 the bituminous-coal measures, have nowhere been observed to thin out 

 owing to overlap, yet in many places Eocene strata are absent, and Miocene 

 beds are found resting on pre-Tertiary rocks. The question of whether 

 this increased extent of the pre-Eocene unconformity is due wholly to 

 overlap, or in part to erosion of the bituminous-coal measures, has already 

 been discussed, and decided in favour of the latter supposition. 



Summary and Conclusions. 



The evidence of unconformity at. two horizons, one pre-Tertiary and 

 the other post-Miocene, is clear and unmistakable. In the case of a third 

 unconformity — that between the Eocene and the Miocene — certainty is 

 wanting, but the available data strongly favour a stratigraphical break. 

 In view of the importance of the matter from an economic point of view, 

 it may be as well roughly to summarize the evidence both for and against 

 this pre-Miocene unconformity, and to leave the reader either to form his 

 own conclusion or, if he pleases, to preserve an open mind. Unconformity 

 is supported by the occurrence in Miocene rocks of water-worn pebbles of 

 coal and of carbonaceous shale almost certainly derived from Eocene coal- 

 measures ; by marked discordance of dip between Miocene strata and 

 Hawk's Crag breccia at Brighton ; by a number of apparently unconform- 

 able contacts between Eocene and Miocene strata ; and by the strong over- 

 lap of the Miocene rocks on the pre-Tertiary land-surface. 



On the other hand, it is just possible that the coal pebbles are a product 

 of contemporaneous erosion ; that the discordance in dip between Miocene 

 and Eocene rocks at Brighton has another explanation ; that the appa- 

 rently unconformable contacts between Eocene and Miocene strata can be 

 explained by faulting or in some other way ; and that the strong overlap 

 of the Oamaru rocks on the pre-Tertiary land-surface is wholly due to the 

 bold relief of the land at the beginning of the Eocene, and not at all to 

 unconformity between two Tertiary formations. 



Though the evidence for a stratigraphical break may uot be regarded 

 as conclusive, it is mainly of a positive character, whilst the opposing 

 evidence is largely negative. It is practically certain that considerable 

 earth-movements took place after the formation of the bituminous-coal 

 seams and before the deposition of the Oamaru series. The point in doubt 



