Thomson. — Geology of Middle Clarence and U re Valleys. 337 



being considered unconformable, while the Awatere beds represented a 

 younger Tertiary transgression. Outside the diastropliic district of North 

 Canterbury and East Marlborough, in the South Island at least, no cor- 

 relative beds of similar naturt* and ])osition are known, and I suggested 

 in 1916 that the term " grey marls " if confined to nmdstones following 

 the Weka Pass stone in this district remains a useful geological term, but 

 that its usefulness is destroyed if it is used indiscriminately for Tertiary 

 mudstones of any age or position. 



The " grey marls '" are generally fine-grained or sandy mudstones with 

 little calcareous matter except as actual fossils, although concretions are 

 sometimes found. They form clift's of a grey colour, in opposition to 

 the bluer and generally more calcareous Wanganuian papas of the North 

 Island and of the Awatere series, and frequently exhibit the peculiar 

 conchoidal weathering of indurated but massive mudstones, and seldom 

 show shaly partings. Very fret{uently the beds become more sandy and 

 may be described as nmddy sandstones. Bedding-planes are in general 

 obscure. Fossils are present in almost all exposures, but are often scanty 

 and frequently crumbling. The larger fossils are chiefly molluscs and 

 corals, while Foraminifera are in places plentiful. Echinoids are occasion- 

 ally present, but brachiopods are almost absent. 



In the Middle Clarence area I have studied these beds only in the 

 Mead, Limburne. and Dee Gorges, and must rely on McKay's descriptions 

 for other parts of the area. 



Mead Gorge. — McKay describes the beds as " about 400 ft. of greenish- 

 grey sandy marls, which contain concretions and a few fossils, not 

 suflficiently well preserved to be of value in determining the age of the 

 beds. Casts of Deutaliuni and Solenella were obtained, and fragments of 

 a nacreous shell are abundant in some part of the softer beds." 



The Mead Gorge flares out in crossing the '' grey marls " and forms a 

 sort of basin-shaped excavation, the sides of which are in great part 

 .' lijjped. A continuous section is exposed only at the top of the cliffs on 

 the south side, but the cliffs are here practically unscalable. The junction 

 with the Weka Pass stone is well exposed on the north side, the latter 

 rock striking N. 18° E. and dipping 55° to the east. It is an argillaceous 

 limestone, somewhat shaly, and passes up quite gradually into hard, 

 somewhat fissile mudstones, of which only about 30 ft. are here exposed. 

 On the soiith side the lower part of the " grey marls " is covered by 

 slipped material, except near the top of the cliff. The upper part on this 

 side appears to be quite conformable to the overlying great Marlborough 

 conglomerate, but shows no well-defined bedding. There are a number 

 of small greywacke pebbles in the uppermost part of the "' grey marls," 

 seeming to establish a passage to the conglomerate. 



Fossils are present in the upper part of the " grey marls," both isolated 

 and in concretionary blocks. It appears possible, however, that these 

 l:)locks are not concretions in situ but are derived, for they are frequently 

 angular in outline and exhibit the broken-oft' ends of shells on their 

 exteriors. The blocks are small at a horizon 10 ft. from the top, but are 

 as much as 18 in. in diameter at 100 ft. from the top. There are in 

 addition many ellipsoidal and rope-like masses which appear to be con- 

 cretions in situ. 



From a horizon 130 ft. from the top I collected Canlium patulum 

 Hutt. (?). A horizon 100 ft. below the top yielded VoJuta arahka ]Mart., 

 Dentalium mantelU Zitt., and Paphia curta Hutt. At 30 ft. I collected 



