Thomson. — Geology of Middle' Clarence and Ure Valleys. 341 



McKay's conception of the conglomerate as post-Miocene necessarilv 

 involved a considerable unconformity between it and the " grey marls," 

 whicli he classed as Cretaceo-Tertiary. Perhaps in consequence of this 

 he did not examine the junctions between the two rocks very carefully. 

 In all liis sections the conglomerate is shown as resting unconformably 

 on the " grev marls," generally v\-ith very slight truncation of the beds of 

 the latter, but in the Mead Gorge the truncation shown is very marked. 

 Hector's section shows the conglomerate overlapping the " grey marls " 

 on to the Weka Pass stone, but this is in marked disagreement with his 

 ])lan Dr. Cotton and I examined carefully all the exposed junctions in 

 the ]\Iead and Dee Gorges and could find no evidence of unconformity. 

 Jf there is anv, it is more probably between the up])er and lower parts 

 of the rocks above described as " grey marls," for a violent unconformity 

 may escape recognition in mudstone cliffs. The upper " grey marls " 

 are certainly Oamaruian, so that even were an unconformity present below 

 them the conglomerate would still be much older than McKay supposed. 



Cotton (1914) has discussed the question of the unconformity of the 

 conglomerate fully, and has shown how a false impression of unconformity 

 in tlie Mead Gorge may be received. In the first ])lace, owing to the 

 widening-out of the gorge wdiere it crosses the outcrop of the weak " grev 

 marls," the junction has an apparent dip whicli the eye is tempted to 

 compare with the true dip of the Weka Pass stone as seen below on dip 

 slopes. In the second ])lace, the surface of the junction, originally plane, 

 is now broken by a number of small faults, giving it an undulating form 

 in section. Cotton records the strike of the junction plane as N. 25° E.. 

 and the di]) as 47° to the west-north-west. My observation of the strike of 

 the Weka Pass stone was N. 18° E., and the dip 55° to the west-north-west. 

 The slight differences between these figures are less than occur within 

 similar thicknesses of the Aniuri limestone lower down in the section. 



A further argument in favour of conformity is the presence of grey- 

 wacke pebbles and of plant-bearing sandstones in the upper " grey marls " 

 of the ]\]ead section, and of conglomerate lenses in a similar position in 

 the Dee section. Plector has described similar plant-bearing sandston(>s 

 at the base of the conglomerate in Shades (? Deadman's) Creek and in 

 Heaver's Creek. In the latter locality I was imable to separate these from 

 the upper " grey marls." In the Mead section their intercalation with 

 Oamaruian mudstones is certain. 



In almost all exposures McKay records the presence of crystalline 

 rocks l)elonging to the intrusive dykes which seam the pre-Notocene rocks 

 in the Tapuaenuku massif. A careful examination of all the exposures 

 in the Mead, Dee, and various exposures near Kekerangu convinced 

 Dr. Cotton and myself that these rocks are practically absent, or at least 

 rare. In almost all exposures there are small boulders of doleritic and 

 porph^-ritic igneous rocks which bear a closer resemblance to the Clarentian 

 volcanic lavas of the Clarence and AAvatere Valleys than to the intrusives, 

 and syenites such as compose the bulk of the upper part of the Tapuaenuku 

 massif appear to be quite absent. McKay considered that the crystalline 

 material in the gravels of the Swale and Ure Rivers was derived from the 

 conglomerate ; but in the latter river this is certainly not the case, 

 the bulk of the material coming from the dark, coarse-grained dolerite 

 of the Blue Mountain, of the existence of which McKay was not aware. 



Mead Gorge. — As already mentioned, the upper part of the " grev 

 marls " contains pebbles of greywacke, and concretionary masses with 

 fossils which may possibly be derived boulders. Cotton describes the 



