Fox. — The Waitemata Series. 4(55 



formability. He wrote : " Great potholes, similar to that 

 now occupied by the North Shore Lake [Lake Takapuna] , 

 were formed, and these were filled by Pliocene beds composed 

 chiefly of volcanic agglomerates"* — i.e., by the different out- 

 crops of the Cheltenham breccia, each outcrop marking, I 

 suppose, the site of a former lake. Sir James Hector also 

 gave a section at the Wairau Creek to show that the breccia 

 lay unconformably on the Waitemata sandstones. I have 

 repeatedly examined this spot and can find no section closely 

 resembling the one given, so that I think some other locality 

 was probably intended. The breccia does, indeed, occur at the 

 "Wairau Creek, but it appears unconformable to the sand- 

 stones from which the fine specimen of Pentacrinvs now in 

 the Auckland Museum was obtained. This appearance of 

 unconformability is, I believe, deceptive, partly due to the 

 effects of current- bedding at the base of the breccia, partly to 

 a series of small faults which obscure the section, and partly 

 to distortion of beds of unequal hardness, which is the reason 

 given by Mr. Park. Mr. Lamplugh has shown how a " crush 

 breccia" may be formed where the strata shade off into one 

 another. Here, however, we have beds of quite distinct hard- 

 ness, and in that case an appearance of unconformability is 

 generally the result of crushing. 



In reply to Sir James Hector Mr. Park wrote: "It 

 should, however, be pointed out that wherever the strata 

 occupy a horizontal or undulating position the breccia is 

 seen to be interbedded with and quite conformable to the 

 adjacent beds, and at its base is frequently more or less false 

 bedded with the underlying clays and sandstones. On the 

 other hand, at points of severe local disturbance where the 

 breccia is present the softer and more yielding clays and soft 

 sandstones have in many instances been crushed and con- 

 torted and often turned over the more compact, heavy, and 

 unyielding ash-bed, thus giving rise to apparent unconformity." 



Mr. Park's section shows how an inverted-trough fault 

 may produce an appearance of unconformability in beds of 

 markedly unequal hardness. On the weathered face of the 

 cliff the faults and fault breccia are by no means as prominent 

 as they are in his drawing. C is the bed from which Penta- 

 crinus was obtained. In a spot where the underlying sand- 

 stones were exposed an inverted-trough fault might still more 

 easily cause a deceptive outline. 



It is also quite true, as Mr. Park observes, that the un- 

 conformable appearance generally coincides with an area of 

 distortion ; but this is not universally the case, as at the 

 Manukau Harbour. 



* Geological Reports, 18$5, p. xxxviii., woodcut. 

 30 



