Thomson. — Geology of Middle Waipani and IVe/.-a Pass Distriet . 345 



The question was raised by Holmes (c/. Hector. 1869) whether the 

 saurian " boulders " were not derived, or at least '' deposited in the bed as 

 rolled masses," since in some of them the saurian bones reach to the 

 exterior, and appear there to be water- worn'. Von Haast (1871) confirmed 

 this observation, but concluded that the concretions were in situ. McKay 

 (1892, p. 99) was therefore led to describe the boulders in great detail to 

 explain this phenomenon : " They are often encased in 5 in. to 6 in. of 

 impure cone-in-cone limestone, or by an envelope of similar thickness com- 

 posed of sandy calcareous matter, preserving fucoid stems so abundantly 

 that these must have formed a perfect envelope round the nucleus and 

 greater mass of the concretion. Interior to this cone-in-cone or fucoidal 

 covering the concretion is a hard greyish-blue limestone rock, and the 

 remains of various species of saurians when present for the most part 

 appear near the centre ; but in cases in which considerable and connected 

 portions of a saurian skeleton occur the bones are sometimes found through 

 the whole diameter of the concretion proper, and into the cone-in-cone 

 limestone or fucoidal envelope that surrounds the harder central portion. 

 From the high cliff on the left bank of the river below the junction of Pirau 

 Burn, concretions often fall into the channel of the river at its base, and in 

 several- cases, as at present can be seen, they l^ave embedded in the marly 

 greensands one-half or less of the cone-in-cone, more rarely of the fucoidal, 

 envelope ; also boulders may be seen in situ from which one-half of the 

 cone-in-cone envelope has been loosened and fallen off, leaving the con- 

 cretion beneath perfectly round and smooth. When the calcareous matter 

 accreting to form the boulder has from an}' cause been insufficient to 

 include the whole of the remains within the concretion proper, some of the 

 bones are fractured or jointed along the line joining the boulder and itS' 

 envelope, and the bones thus appearing at the surface are polished as 

 though the boulder had been formed mechanically, and transported to the 

 position it liow or lately occupied by the action of running wat^r." 



In the creek called by McKay the Pirau Burn the sands immediately 

 above the Ostrea bed are well bedded by the interposition of numerous 

 carbonaceous shaly partings, and present a great similarity to the sands 

 under the Ostrea bed farther to the north-east. 



The sulphur mudstones forming the upper part of the " saurian beds " 

 are followed by the Waipara greensand, which may here be divided into a 

 lower and an upper group. The lower group consists of 75 ft. of alternat- 

 ing hard and soft greensandstopes, the hard bauds being 1 ft. to 2 ft. in 

 thickness and an average of 7 ft. apart. The hard parts are not continuous, 

 but have a concretionary appearance (Plate XVIII, fig. 1). They have 

 generally been described as calcareous, but show little eft'ervescence with 

 acid, and in thin section are found to consist of rounded grains of quartz 

 and glauconite, accompanied by small pyritized fragments of organisms 

 (probably radiolarian), set in a fine-grained granular matrix which is not 

 birefringent. In hand-specimens the rock is mottled green and purple- 

 grey. TJie upper group, 110 ft. thick, consists of softer, very dark green- 

 sands with a good deal of argillaceous matter and frequently with a shaly 

 parting. In the clift' on the south side at the upper end of the large 

 river-meander these pass quite gradually into the succeeding glauconitic 

 mudstones, but in the cliff on the north side at the junction with Birch 

 Hollow there are a few bands of hard greensandstone at the top, similar 

 to those of the lower series. These u]:)per greensands contain many pyrite 

 concretions and have a marked yellow efflorescence. 



